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FLEX 6809 Relocating Assembler

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1. 32 Simulated 6800 Instructions ABA Add B to A CBA Compare B to A CLC Clear carry bit CLI Clear interrupt mask CLV Clear overflow bit DES Decrement stack pointer DEX Decrement X INS Increment stack pointer INX Increment X SBA Subtract B from A SEC Set carry bit SEI Set interrupt mask SEV Set overflow bit TAB Transfer A to B TAP Transfer A to CC TBA Transfer B to A TPA Transfer CC to A TSX Transfer S to X TXS Transfer X to S WAI Wait for interrupt 33 FLEX 6809 Relocating Assembler FLEX 6809 Relocating Assembler Simulated 6801 Mnemonics ASLD LSRD PSHX PULX LDAD STAD Arithmetic shift left D Logical shift right D Push the X register Pull the X register Load accumulator D from memory Store accumulator D into memory Convenience mnemonics BEC LBEC BES LBES CLF CLZ SEF SEZ Branch short or long if error clear Branch short or long if error set Clear FIRQ interrupt mask Clear zero condition code bit Set FIRQ interrupt mask Set zero condition code bit 34 FLEX 6809 Relocating Assembler V STANDARD DIRECTIVES OR PSEUDO OPS Besides the standard machine language mnemonics the relocating assembler supports several directives or pseudo ops These are instructions for the assembler to perform certain operations and are not directly assembled into code There are three types of directives in this assembler those associated with macros those associated with
2. BLS short or FORM BLT long if dd LBGE long if dd LBGT long if dd LBHI long if dd LBHS long if dd LBLE long if dd LBLO long if dd LBLS long if dd LBLT greater than or equal dddd greater than dddd higher dddd higher or same dddd less than or equal to dddd lower dddd lower or same dddd less than dddd 28 BMI BNE BPL BRA BRN BSR BVC BVS CLR CMP COM CWAI DAA DEC LBMI LBNE LBPL LBRA LBRN LBSR LBVC LBVS Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Clear short or FORM BMI short or FORM BNE short or FORM BPL short or FORM BRA short or FORM BRN short or FORM BSR short or FORM BVC short or FORM BVS FLEX 6809 Relocating Assembler long if minus dd LBMI long if dd LBNE long if dd LBPL dddd not equal dddd plus dddd long always dd LBRA dddd long never dd LBRN long to dd LBSR long if dd LBVC long if dd LBVS dddd subroutine dddd overflow clear dddd overflow set dddd SOURCE FORM CLRA CLRB CLR 6800 ALTERNATES CLR A CLR B Compare SOURCE FORM CMPA P CMPB P CMPD P CMPX P CMPY P CMPU P CMPS P 6800 ALTERNATES CMP A P CMP B P CPX P Complement One s complem
3. IV THE INSTRUCTION SET This section is a quick introduction to the 6809 architecture and insruction set It is by no means complete The intention is to familiarize the user who is already proficient at 6800 assembly language programming with the basic structure of 6809 assembly language For more complete details on the 6809 instruction set you should obtain the proper documentation from the hardware manufacturer Programming Model The 6809 microprocessor has 9 registers that are accessible by the programmer Four of these are 8 bit registers while the other five are 16 bit registers Two of the 8 bit registers can in some instances be referenced as one 16 bit registers The registers are as follows The A accumulator A 8 bit The B accumulator B 8 bit The Condition Code register CC 8 bit The Direct Page register DP 8 bit The X index register X 16 bit The Y index register Y 16 bit The User stack pointer U 16 bit The System stack pointer S 16 bit The Program Counter PC 16 bit The A and B accumulators can often be referenced as one 16 bit register represented by a _ D for Double accumulator In these cases the A accumulator is the most significant half The Addressing Modes There are several possible addressing modes in the 6809 instruction set One of the best features of the 6809 is the consistency or regularity built into the instruction set For the most part any instruction which addresses
4. conditional assembly and those which generally can be used anywhere which we shall call standard directives This section is devoted to descriptions of these directives which are briefly listed here ABS SET RPT ORG REG LIB END SETDP GLOBAL RMB PAG DEFINE and ENDDEF RZB SPC EXT FCB TTL NAME FDB STTL COMMON and ENDCOM FEC ERR OPT EQU Descriptions of each directive and its use follow AB The ABS or Absolute directive signals the relocating assembler to assemble the following module as an absolute module This means that there will be no relocatable expressions The ABS directive should appear in the source module before any other code in the source module Its syntax is as follows ABS There should be no label or operand Use the ABS directive when a module has to be loaded at a particular location it is not to be assigned a load address by the linking loader ORG The ORG statement is used to set a new code Origin This simply means that a new address is set into the location counter or program counter so that subsequent code will be placed at the new location The form is as follows 35 FLEX 6809 Relocating Assembler ORG lt expression gt No label may be placed on an ORG statement and no code is produced If no ORG statement appears in the source an origin of 0000 is assumed The ORG directive should be used only in absolute modules they are ignored and flagged as errors in relocatable modules All exp
5. extl is an external symbol rell rel2 have the same meaning as above in the previous examples the following examples are external rell rel2 extl rel2trel1 5 ext1 3 3 rel2 rel11 extl 19 FLEX 6809 Relocating Assembler EXPRESSION OPERATORS As mentioned previously the four classes of operators are arithmetic logical relational and shift These operators permit assembly time Operations such as addition or division to take place Assembly time means that the expression is evaluated during the assembly and the result becomes a permanent part of your program Realize that many of these operators will only apply to absolute symbols and expressions It does not make sense to multiply a relocatable or external value at assembly time Only the and operators can apply to relocatable and external symbols and expressions all of the other operators can be used with absolute symbols and expressions a ARITHMETIC OPERATORS The arithmetic operators are as follows Operator Meaning Unary or binary addition Unary or binary subtraction Multiplication Division any remainder is discarded b LOGICAL OPERATORS The logical operators are as follows Operator Meaning Logical OR operator Logical NOT operator gt gt Shift right operator lt lt Shift left operator Logical AND operator l The logical operations are full 16 bit operations In other words for the AND operation every bit from the first operand
6. one single minus sign or two double minus sign The resulting value with no offset is used as the effective address Example LDA 0 U decrements U by 1 then loads A from address in U LDU S decrements S by 2 then loads U from address in S Further Addressing Modes Indexed Indirect Addressing All the Indexed Addressing modes above can also be used in an indirect fashion by enclosing the operand in square brackets When this is done the effective address as described in all the above modes is no longer the final effective address Instead the two bytes pointed to by that address are used as the effective address Examples LDA X loads A from the address pointed to by X LDX D U loads X from the address pointed to by U D If auto increment or auto decrement addressing is done in an indirect fashion they must be a double increment two plus signs or double decrement two minus signs PC Relative Addressing Indexing may be done from the PC register just as from the X Y U or S The general use of indexing from the PC register is to address some value in a position independent manner Thus if we address some value at the current PC plus 10 no matter where the program executes the value will always be addressed The programmer does not usually know what that constant offset should be he knows the address of the value he wants to access as an absolute value for the program as assembled Thus a mechanism has been included
7. a label BUFPNT which is at memory location 0010 Normally the instruction in an absolute module LDX BUFPNT would be assembled with direct addressing If we wished to force extended addressing we could simply enter LDX gt BUFPNT and the assembler would use extended addressing Relocatable modules will use extended addressing as the normal default The same capability exists for forcing direct addressing by preceding the operand with a less than sign lt For example LDX lt BUFPNT would force direct addressing In some cases such as PC Relative addressing the forcing of direct addressing for relocatable and external expressions will be ignored Note that in both cases the greater than or less than sign must be the first character in the operand 26 FLEX 6809 Relocating Assembler The Assembler Instruction Set This section contains a brief listing of all the mnemonics accepted by the 6809 assembler They are listed in four sections standard 6809 with alternate 6800 6800 mnemonics not found in 6809 6801 mnemonics and non standard convenience mnemonics Before the listing we must setup some notational conventions P Operand containing immediate extended direct or indexed addressing Q Operand containing extended direct or indexed addressing T Operand containing indexed addressing only R Any register specification A B X Y U S PC CC DP or D dd 8 bit data value dddd 16 bit dat
8. and outputting object code if desired The source may be supplied in free format as described below Each line of source consists of the actual source statement terminated with a carriage return 0D hex The source must be comprised of ASCII characters with their parity or 8th bit cleared to zero Special meaning is attached to many of these characters as will be described later Control characters 00 to 1F hex other than the carriage return 0D are prohibited from being in the actual source statement part of the line Their inclusion in the source statement will produce undefined results Each source line is comprised of up to four fields Label Opcode Operand and Comment With two exceptions every line must have an opcode while the other fields may or may not be optional These two exceptions are 1 Comment Lines may be inserted anywhere in the source and are ignored by the assembler during object code production Comment lines may be either of two types a Any line beginning with an asterisk hex 2A or semicolon hex 3B in column one b A null line or a line containing only a carriage return While this line can contain no text it is still considered a comment line as it causes a space in the output listing 2 Lines which contain a label but no opcode or operand field 13 FLEX 6809 Relocating Assembler SOURCE STATEMENT FIELDS The four fields are described here along with their format specifications The fields are fre
9. elements 18 1 FLEX 6809 Relocating Assembler The expression does not contain an even number of relocatable elements 2 All the relocatable elements but one must be organized in 3 For pairs that cancel each other That is for all but one each relocatable element or multiple must be canceled by another relocatable element or multiple The elements that form a pair need not be contiguous in the expression The uncanceled element can have either positive or negative relocation example rell and rel2 are relocatable symbols from a module the following examples are relocatable rel2 3 5 negative relocation rell 3 rell rel2 re11 1 PC Designator c External Expressions An expression is external if its value depends upon the value of a symbol defined outside of the current source module Either an external expression consists of a single external symbol or under both of the following conditions an external expression may consist of an external symbol relocatable elements and absolute elements 1 2 The expression contains an even number of relocatable elements The relocatable elements must cancel each other That is each relocatable element or multiple in a module must be canceled by another relocatable element In other words pairs of relocatable elements must have signs that oppose each other The elements that form a pair need not be contiguous in the expression For example
10. in the header at the top of each output page The assembler normally picks up the current date from FLEX and prints it in the header This option causes the date to be omitted F Enable debug or Fix mode There are two forms of line comments One begins with an asterisk the other with a semicolon both in the first column of the source line If the comment begins with a semicolon the F option will instruct the assembler to ignore the semicolon and process the line as though the semicolon never existed The asterisk in the first column of a source line will always denote a comment regardless of the state of this option G Turns off printing of multiple line object code instructions Certain directives FCB FDC and FCC can produce several lines of output listing for only one instruction line This option prints the first line of output from such an instruction the line which contains the source but suppresses the printing of the subsequent lines which contain only object code information I Enable the appending of all internal symbols Normally the relocating assembler will append only the global symbol table information to each binary output module This is then used by the linking loader to resolve externals By specifying this option all of a source module s symbol table information is appended to its binary module The one exception to this is symbol table information for external symbols this is never written out in the symb
11. it expands into quite a bit of source if the macro expansions are being listed because the 3rd 4th and 5th line are expanded for each of the one hundred times through However only one hundred bytes of object code are actually produced since lines 3 and 5 don t produce code If a label is specified on a line in the macro you will receive a multiply defined symbol error if the macro is called more than once There is a way to get around this shortcoming that is somewhat crude but effective That is to use a dummy parameter as a label and require the programmer to supply a different label name as that parameter each time the macro is called For example consider the following example SHIFT MACRO PSHS D LDA amp l LDB amp 2 amp 3 ROLA DECB BNE amp 3 STA amp l PULS D ENDM 58 FLEX 6809 Relocating Assembler Now if this macro was called with the line SHIFT FLAG 3 CALL1 The resulting macro expansion would look like PSHS D LDA FLAG LDB 3 CALL1 ROLA DECB BNE CALL1 STA FLAG PULS D There is no problem here but if the macro were called again with the same string for parameter 3 CALL1 a multiply defined symbol error would result Thus any subsequent calls to SHIFT must have a unique string for parameter 3 such as CALL2 CALL3 etc Of course the easiest way to do this is by using local labels within the macro Important Notes on MACROS 1 A macro must be defined before the first call to i
12. memory can use any of the addressing modes available It is not necessary to remember which instructions can use which addressing modes etc The addressing modes and a brief description of each follow 22 1 2 3 4 5 6 FLEX 6809 Relocating Assembler Inherent Inherent addressing refers to those instructions which have no addressing associated with them Example ABX add B accumulator to X Accumulator Accumulator addressing is done in those instructions which can specify the A or B accumulator In some cases this may be the 16 bit D accumulator Example DECA decrement the A accumulator Immediate In Immediate addressing the byte or bytes following the opcode are the information being addressed These byte or bytes are specified as part of the instruction Example LDA 8 load immediate value 8 into A Relative Long and Short In Relative addressing the value of the byte s immediately following the opcode 1 if short 2 if long are added as a two s complement number to the current value of the program counter PC register to produce a new PC location Note that only long branches are allowed for external expressions In the source code the programmer specifies the desired address to which execution should be transferred and the assembler determines the correct offset to place after the opcode Example LBRA THERE the program will branch to THERE Extended In Extended addressing the two bytes 1
13. or item is individually AND ed with its corresponding bit from the second operand or item The shift operators shift the left term the number of places indicated by the right term Zeroes are shifted in and bits shifted out are lost c RELATIONAL OPERATORS The relational operators are as follows 20 FLEX 6809 Relocating Assembler Operator Meaning Equal lt Less than gt Greater than lt gt Not equal lt Less than or equal gt Greater than or equal The relational operations yield a true false result If the evaluation of the relation is true the resulting value will be all ones If false the resulting value will be all zeros Relational operations are generally used in conjunction with conditional assembly as shown in that section OPERATOR PRECEDENCE Certain operators take precedence over others in an expression This precedence can be overcome by use of parentheses If there is more than one operator of the same priority level and no parentheses to indicate the order in which they should be evaluated then the operations are carried out in a left to right order The following list classifies the operators in order of precedence highest priority first 1 Parenthesized expressions 2 Unary and 3 Shift operators 4 Multiply and Divide 5 Binary Addition and Subtraction 6 Relational Operators 7 Logical NOT Operator 8 Logical AND and OR Operators 2 1 FLEX 6809 Relocating Assembler
14. relocatable binary disk file Since no name was specified the output binary file will assume the same name as the input source file specified but with a REL extension If such a file already exists you will be asked FLEX 6809 Relocating Assembler Delete Old Binary Y N to which you may respond Y which will delete the existing file and continue to create the new file or N which will immediately terminate the assembly returning to FLEX with the old binary file remaining intact If you wish to create a binary file by another name or extension you may do so by placing the desired file specification on the command line as follows RELASMB lt input file spec gt lt binary file spec gt lt option list gt This binary file specification will default to a REL extension and to the assigned working drive If a file by that name already exists on the specified drive you will be prompted as described above A temporary scratch file is created to hold the external and relocation records that are produced during assembly This file is only created if a binary file is being produced The name of this file will be the name of the source input file with a SCR extension If this file should happen to exist the assembler will prompt the user Delete Old Scratch File Y N A response of N will abort the assembly Normally this file will be automatically created and deleted by the assembler This scratch file will exist on the
15. same drive as the binary output file Please ensure that there is room on the disk for the binary output file this temporary scratch file and the cross reference information file if it is selected Specifying Assembly Options Now we shall go one step further and add a set of single character option flags which may be set on the command line as follows RELASMB lt input file spec gt lt binary file spec gt lt option list gt The square brackets indicate that the binary file spec and the option list are optional The plus sign is required to separate the option list from the file specifications The lt option list gt is a set of single character flags which either enable or disable a particular option In all cases they reverse the sense of the particular option from its default sense There may be any number of options specified and they may be specified in any order There may not be spaces within the option list Following is a list of the available options and what they represent FLEX 6809 Relocating Assembler A Causes the absolute address of all relative branches to be printed in the object code field of the assembled output listing B Do not create a binary file on the disk No binary file will be created even if a binary file name is specified This is useful when assembling a program to check for errors before the final program is completed or when obtaining a printed source listing D Suppress printing of the date
16. that the code is to be absolute with an ABS directive 68 FLEX 6809 Relocating Assembler As stated in a previous section the total number of errors is reported at the end of the assembly and if warning messages are enabled the number of warnings are also output 69 FLEX 6809 Relocating Assembler X ADAPTING TO YOUR SYSTEM In general if you have FLEX up and running and have at least 16K of user memory there will be no need for any adapting whatsoever Some users however always feel the need to modify certain things and this section describes how to make all the changes which we felt might be desired and which would be feasible With the exception of MEMEND these changes must all be made to the object code of the assembler This can be done by loading the assembler with a GET RELASMB CMD command making the desired changes in memory ard saving the result on disk with the SAVE command MEMEND If using the automatic table setup which the assembler performs for you the MEMEND value in FLEX should be set to the last address which the assembler should use FLEX initializes MEMEND to the actual end of user memory You may have an application where you don t want this to be the case If so set MEMEND manually before executing the assembler EXIT ADDRESS When the assembler is finished it jumps into FLEX s warm start If you wish it to exit to some other address place that address at location 02FC OUTPUT
17. to only six characters RELASMB 0 TEST BAK GSOBNP26 This command performs just like the last with two exceptions First the assembler itself is loaded from the whatever the assigned system drive is Second the assembled listing output does not begin until the assembler reaches page number 26 0 RELASMB 0 RELASMB 0 RELASMB GW MINI ASSEMBLER FOR 5 DISK This command looks a little confusing but it was done to accentuate the method in which default extensions work The assembler itself a file called RELASMB CMD is loaded from drive 0 the file called RELASMB TXT found on drive 0 is assembled and a binary file is produced on drive 0 by the name RELASMB REL Note that it was not necessary to specify the binary file name in this case since RELASMB REL is what the default would have been The assembled listing is output with multiple line code generation suppressed and warning messages suppressed There are two parameters which may be passed into the source listing The first is the single word MINI The second parameter is the entire string ASSEMBLER FOR 5 ODISK excluding the single quote delimiters everything starting with the A and ending with the K 12 FLEX 6809 Relocating Assembler III ASSEMBLER OPERATION amp SOURCE LINE COMPONENTS The FLEX Relocating Assembler is a 2 pass assembler During pass one a symbolic reference table is constructed and in pass two the code is actually assembled printing a listing
18. to set up the necessary tables and buffers manually you may do so This requires that you supply the starting and ending addresses of the five tables described in the section on special features and set a byte called MANUAL to some non zero value This MANUAL byte is located at 0003 and is currently equal to zero The assembler tests this byte and if zero performs automatic table setup If non zero the assembler picks up the table start and end addresses from the following locations SOURCE BUFFER BEGIN 0004 SOURCE BUFFER END 0006 MACRO NAME TABLE BEGIN 0008 MACRO NAME TABLE END 000A MACRO ACTIVATION BUFFER BEGIN 000C MACRO ACTIVATION BUFFER END 000E MACRO TEXT BUFFER BEGIN 0010 MACRO TEXT BUFFER END 0012 LOCAL LABEL LIST BEGIN 0014 LOCAL LABEL LIST END 0016 SYMBOL TABLE BEGIN 0018 71 FLEX 6809 Relocating Assembler SYMBOL TABLE END 001A NOTES 1 The Macro Name Table and the Symbol Table must be an even multiple of 12 bytes in size 2 The assembler uses a large stack area to maintain all its temporary variables and buffers This stack requires OADO hex bytes of RAM starting at FLEX s MEMEND and growing down from there This implies two things if manually setting up the tables you must leave this space free and if you want to move where the stack resides you must set MEMEND accordingly as the assembler will always place its stack so that it sets up against MEMEND 3 When manually setting up the tables yo
19. which do not require relocation are absolute addresses their values remain the same regardless of the position of the program in memory Since the loader does not have access to the source text it cannot determine if an address field is absolute or relative relocatable In fact it cannot distinguish addresses from data Therefore the assembler must indicate to the loader the address fields which require relocation This communication is accomplished through relocation records which are appended to the object code file produced by the assembler Such a file is called a relocatable object code module Linking Loaders As discussed previously it is necessary or desirable for parts of a program modules to be developed separately Each module must be assembled and tested separately prior to final merging of all the modules During this merging process of the modules it is necessary to resolve references in a module which refer to addresses or data defined in another The resolution of external references is called linking The assembler must provide information to the linker in a manner similar to relocation records concerning the address fields which must be resolved FLEX 6809 Relocating Assembler Since the production of relocation records and external records are similar processes both of these features are often included in a relocating assembler A linking loader is a program which can take the output of a relocating assembl
20. 0005 27 0007 B7 000A 39 IFN 1 0 1 1 ERR NOT A VALID PORT NUMBER ELSE IF 1 0 ACIA EQU E 000 ELSE E004 ACIA EQU 6004 ENDIF ENDIF E004 OUTCH LDB ACIA 02 ANDB 02 F9 BEQ OUTCH E004 STA ACIA RTS END 0 Error s Detected Note that the first page of output is not shown 66 FLEX 6809 Relocating Assembler IX ERROR AND WARNING MESSAGES The assembler supports warning messages and two types of error messages fatal and non fatal A fatal error is one which will cause an immediate termination of the assembly such as not enough memory A non fatal error results in an error message being inserted into the listing and some sort of default code being assembled if the error is in a code producing line The assembly is allowed to continue on non fatal errors Warning messages are handled much like non fatal errors the message is inserted in the output listing and the assembly is allowed to continue These warning messages may be suppressed by the W option in the command line Error messages may not be suppressed All messages are output as English statements not as error numbers These messages announce violations of any of the rules and restrictions set forth in this manual and are therefore essentially self explanatory Error messages are output with three asterisks preceding the message Warning messages are output with two asterisks preceding the message This can be used to quickly locate the messages either by
21. 1 FLEX 6809 Relocating Assembler Fix Mode The relocating assembler has the capability to accept comment lines that begin with either an asterisk or a semicolon If a semicolon is used the F option of the assembler will assume that the comment is a valid instruction to be assembled Therefore the assembler will act as though the semicolon did not exist at all the rest of the information on that line will be assembled For example LABEL1 LDX 2 LDD TEST U With the F option invoked these two lines will be normally assembled This aides in the debugging process Local labels are available in the assembler These local labels allow the programmer to reuse labels over in this way meaningless labels can be substituted with local labels See section three ASSEMBLER OPERATION amp SOURCE LINE COMPONENTS under the description of the label field for more information on local labels 62 FLEX 6809 Relocating Assembler Auto Table Setup The assembler automatically sets up all necessary tables and buffers depending on the amount of memory contained in your system The amount of memory contained is determined by reading the memory end value MEMEND in FLEX The tables or buffers which can vary in size are as follows SYMBOL TABLE This table is where all symbols are maintained during assembly Each entry into the symbol table requires 12 bytes 8 for the name two for the address or value associated with it a
22. 1 1187 1193 1201 1213 1217 1223 1229 1231 1237 1249 1259 1277 1279 1283 1289 1291 1297 1301 1303 1307 1319 1321 1327 1361 1367 1373 1381 1399 1409 1423 1427 1429 1433 1439 1447 1451 1453 1459 1471 1481 1483 1487 1489 1493 1499 1511 1523 1531 1543 1549 1553 1559 1567 1571 1579 1583 1597 1601 1607 1609 1613 1619 1621 1627 1637 1657 1663 1667 1669 1693 1697 1699 1709 1721 1723 1733 1741 1747 1753 1759 1777 1783 1787 1789 1801 1811 1823 1831 1847 1861 1867 1871 1873 1877 1879 1889 1901 1907 1913 1931 1933 1949 1951 1973 1979 1987 1993 1997 1999 2003 2011 2017 2027 2029 2039 2053 2063 2069 2081 2083 2087 2089 2099 2111 2113 2129 2131 2137 2141 2143 2153 2161 2179 2203 2207 2213 2221 2237 2239 73 FLEX 6809 Relocating Assembler NOTES 74
23. 5F CLRB SET COUNT TO ZERO 1004 A6 80 LOOP LDA 0 X GET A CHARACTER 1006 27 04 BEQ DONE IF END OF STRING 1008 5C INCB COUNT THE CHARACTER 1009 7E 1004 JMP LOOP GET NEXT CHARACTER 100C 39 DONE RTS RETURN 100D 48 4F 57 20 STRING FCC HOW MANY CHARS 0 The program segment will work as intended only if it is loaded at 1000 If CNTCHAR was instead loaded at 2000 at the time the JMP instruction is encountered control would transfer to 1004 however we would intend for control to go to 2004 Suppose it is not possible to know the starting location of a program segment Such would be the case if each member of a team of programmers was responsible for developing a program segment Since each segment is being developed independently of the others it is not possible to know where one segment ends and therefore where the next is to begin Position Independence VS Relocatability The 6809 instruction set offers one solution to this problem PC relative addressing uses the Program Counter PC register as an index register in much the same manner as X Y U or S is used as an index register PC relative addressing generates offs ts or indexes based on the current PC value Using this addressing mode the program will work as intended regardless of its position in memory We can make CNTCHR position independent by replacing the JMP instruction with BRA and LDX immediate with LEAX PC offset indexing Our position independent version of CNTC
24. 6 bits following the opcode are used as an absolute memory address value Example LDA 1000 load A from memory location 1000 hex Direct In Direct addressing the single byte 8 bits following the opcode is used as a pointer into a 256 byte window or page of memory The page used for this purpose is the one currently found in the Direct Page register Thus the effective address is a concatenation of the Direct Page register as the most significant half and the byte following the opcode as the least significant half Realize that direct addressing does not make sense for relocatable or external expressions the normal default will be extended Example LDA 22 load A from memory location XX22 where XX represents the contents of the DP register 23 FLEX 6809 Relocating Assembler 7 8 8a 8b 8c Extended Indirect In Extended Indirect addressing the 16 bit value following the opcode is used to point to two bytes in memory which are used as the effective address Example LDA A012 loads A from the address stored at locations A012 and A013 Indexed The Indexed addressing mode of the 6809 is an extremely powerful method of specifying addresses which is in general some sort of offset from the value stored in one of the registers X Y U S or PC There are several forms of indexed addressing which could each be considered an addressing mode in itself We will however discuss each as a subset of Indexed addres
25. CHARACTER ROUTINE As supplied the assembler outputs through FLEX s PUTCHR routine This takes advantage of the escape return sequence in FLEX to pause or terminate an output Tisting If however you wish to output through some user supplied output routine place the address of such a routine at location 02FF This routine should output the character in the A register and return without affecting any registers except the condition codes 70 LINES PER FLEX 6809 Relocating Assembler PAGE If the page mode is selected the assembler automatically places a header at the top of each page with the current page number and performs a page eject at the bottom The number of lines which are output before the page eject occurs including the header lines is set at location 001C in the assembler This value is currently set to 58 lines Change if desired LINE The symbol table output is done with multiple symbols per line Currently there are 5 labels per line If desired this number can be changed by setting the byte at location 001D AUTO FIELD SETTING UP ING COLUMNS As explained in the special features section this assembler performs auto fielding The columns in which the fields are placed are currently set to 10 17 and 27 for the mnemonic operand and comment fields respectively If desired these columns can be changed by altering the three bytes beginning at location 001E THE TABLES MANUALLY If you wish
26. FLEX 6809 Relocating Assembler El Technical Systems Consultants Inc Table of Contents II III IV VI VII VIII IX XI Introduction Getting the System Started Assembler Operation The Instruction Set Standard Directives Conditional Assembly Macros Special Features Error and Warning Messages Adapting to Your System Appendix A List of Prime Numbers from 773 to 2239 siii Page 13 22 35 47 51 60 67 70 73 FLEX 6809 Relocating Assembler I INTRODUCTION This manual describes the operation and use of the 6809 Relocating Mnemonic Assembler for the 6809 FLEX Disk Operating System The assembler accepts all standard Motorola mnemonics for the 6809 instruction set as well as all standard 6800 and 6801 mnemonics Relocation external references macros and conditional assembly are supported as well as numerous other directives for convenient assembler control The assembler executes in two passes and can accept any size file so long as sufficient memory is installed to contain the symbol table Output is in the form of a relocatable binary disk file as well as an assembled listing output which may be routed to a printer or to a disk file through the facilities of FLEX This manual is by no means intended to teach the reader assembly language programming nor even the full details of the 6809 instruction set It assumes the user has a working knowledge of assembly language programming an
27. HR would look like this FLEX 6809 Relocating Assembler KKKK cntchar count the number of characters X in a null terminated string i exit b count of the characters 1000 ORG 1000 1000 30 8D 0009 CNTCHAR LEAX STRING PCR GET ADDR OF STRING 1004 5F CLRB SET COUNT TO ZERO 1005 A6 80 LOOP LDA 0 X GET A CHARACTER 1007 27 03 BEQ DONE IF END OF STRING 1009 5C INCB COUNT THE CHARACTER 100A 20 F9 BRA LOOP GET NEXT CHARACTER 100C 39 DONE RTS RETURN 100D 48 4F 57 20 STRING FCC HOW MANY CHARS 0 Notice that this CNTCHAR contains no references to absolute addresses It will execute as intended regardless of where it is placed in memory In general however position independent code contains more op code bytes and takes longer to execute than absolute code Also the programmer must make an effort not to use certain instructions or restrict usage to particular addressing modes so that the rules of postion independence are not violated All code on the other hand can be considered relocatable when assembled using a Relocating Assembler Relocating Assemblers and Loaders Relocatable code is generated by a relocating assembler in such a way that addresses are not bound to absolute locations at assembly time this binding of the address fields is deferred until load time A Relocating Loader binds the addresses at the time the program is brought into memory loaded to be executed The binding or adjustment of the address fiel
28. NDD clause may not be placed inside another As an example let s take our first example in this section on macros and spruce it up a little Assume we want a macro that will shift the D register to the left x places where x can vary in different calls to the macro The DUP ENDD construct will work nicely for this purpose as seen here ASLDX MACRO DUP amp l ASLB ROLA ENDD ENDM 56 FLEX 6809 Relocating Assembler Now to shift the D register left four places we call the macro with ASLDX 4 To shift it left 12 places we simply use the instruction ASLDX 12 And so on More on MACROS A few more hints on using macros may be of value One important thing to remember is that parameter substitution is merely replacing one string the dummy parameter or amp x with another the parameter string on the calling line You are not passing a value into a macro when you have a parameter of 1000 but rather a string of four characters When the expanded source code of the macro is assembled the string may be considered a value but in the phase of parameter substitution it is merely a string of characters An example macro will help clarify this point TEST MACRO LDA amp 1 comment field is here LDB L amp l NOP parameters can even be NOP substituted into NOP comments amp 2 amp 3 or they can be a mnemonic amp 4 TST M amp 1M or label or inside a string ENDM Now if this macro were called with the following comman
29. a value 6809 Mnemonics with 6800 Alternates ABX Add B into X SOURCE FORM ABX ADC Add with carry into register SOURCE FORM ADCA P ADCB P 6800 ALTERNATES ADC A P ADC B P ADD Add into register SOURCE FORM ADDA P ADDB P ADDD P 6800 ALTERNATES ADD A P ADD B P AND Logical AND into register SOURCE FORM ANDA P ANDB P 6800 ALTERNATES AND A P AND B P ANDCC Logical AND immediate into CC SOURCE FORM ANDCC dd 27 FLEX 6809 Relocating Assembler ASL ASR BCC BCS BEQ BGE BGT BHI LBCC LBCS LBEQ LBGE LBGT LBHI BHS LBHS BIT BLE BLO BLS BLT LBLE LBLO LBLS LBLT Arithmetic shift left SOURCE FORM ASLA ASLB ASL Q 6800 ALTERNATES ASL A ASL B Arithmetic shift right SOURCE FORM ASRA ASRB ASR Q 6800 ALTERNATES ASR A ASR B Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE short or long if carry clear FORM BCC dd LBCC dddd short or long if carry set FORM BCS dd LBCS dddd short or long if equal FORM BEQ dd LBEQ dddd short or FORM BGE short or FORM BGT short or FORM BHI short or FORM BHS Bit test SOURCE FORM BITA P BITB P 6800 ALTERNATES BIT A P BIT B P Branch SOURCE Branch SOURCE Branch SOURCE Branch SOURCE short or FORM BLE short or FORM BLO short or FORM
30. ation The default drive is the assigned working drive and the default extension is TXT Any END statements found in the file called by the LIB directive are ignored The LIB directive line itself does not appear in the output listing Any number of LIB instructions may appear in a source listing It is also possible to nest LIB files up to 12 levels Nesting refers to the process of placing a LIB directive within the source that is called up by another LIB directive In other words one LIB file may call another If nested LIB files must come from the same drive GLOBAL The GLOBAL directive is used in relocatable modules to inform the assembler that the symbols declared global should be passed on to the linking loader The syntax of the GLOBAL directive is GLOBAL lt label1l gt lt label2 gt 42 FLEX 6809 Relocating Assembler Where labell label2 etc represent the symbolic names of the labels to be declared as global each label should be separated by a comma Realize the GLOBAL directives must occur before the use or definition of the symbol Normally declare global symbols at the beginning of the source module Macros and local labels cannot be declared global DEFINE and ENDDEF These are convenience directives that work much the way GLOBAL works The DEFINE directive informs the assembler that all labels declared in the label field will also be declared as global symbols This define mode will be in eff
31. attempted that is illegal inside a macro or vice versa The PHASING ERROR DETECTED message is reported if the assembler detects an incongruity in addresses between pass one and two Chances of this occurring are small but the assembler will report such an error at the first detection Phasing errors are only detected on lines which contain a label Possible FATAL error messages are ILLEGAL FILE NAME NO SUCH FILE ILLEGAL OPTION SPECIFIED INSUFFICIENT MEMORY MACRO OVERFLOW The first three are associated with errors in the command line The INSUFFICIENT MEMORY message is issued when automatic table setup is enabled and there is not at least 3K of buffer area The MACRO OVERFLOW message occurs when any of the macro buffers is overflowed Possible warning messages are as follows FORCED ADDRESS TRUNCATED IMMEDIATE VALUE TRUNCATED ILLOGICAL FORCING IGNORED NO PRECEDING ABS ORG IGNORED The first warning is printed if an address is forced to 8 bits with the lt character and must be truncated to fit The second occurs on lines where an immediate value must be truncated to fit in 8 bits For example LDB 42E5 would result in such a warning The third is issued if address length forcing with the lt or the gt is done in an operand where not possible For example the instruction LDB lt BUFCNT would result in such a warning Finally the fourth occurs when an ORG is put into code without first informing the assembler
32. conform to the rules for any other assembly language label since it is found in the label field It is in fact a standard label which goes into the symbol table and can be used in other statement s operands like any other label 54 FLEX 6809 Relocating Assembler Ignoring a Dummy Parameter There may be times when a programmer wishes to have an ampersand followed by a number in a macro which is not a dummy parameter and should therefore not be replaced with a parameter string An example would be an expression where the value of MASK was to be logically anded with the number 4 The expression would appear like MASK amp 4 If this expression were in a macro upon expansion the amp 4 would be replaced with the fourth parameter on the calling line It is possible to prevent this however by preceding the ampersand with a backslash like this MASK amp 4 When the assembler expands the macro containing this expression it will recognize the backslash remove it and leave the ampersand and following number intact Another case where this can be useful is when a macro is defined within a macro that is possible and you wish to place dummy parameters in the inner macro The EXITM Directive Sometimes it is desireable to exit a macro prematurely The EXITM directive permits just that During expansion of a macro when an EXITM command is encountered the assembler immediately skips to the ENDM statement and terminates the expa
33. consists of simply placing its name in the mnemonic field of a source line When the assembler sees the above call it realizes that the instruction is not a standard 6809 mnemonic but rather a macro that has been previously defined The assembler will then replace the asld4 with the lines which make up the body of that macro or expand the macro The result would be the following assembled code LDA VALUE LDB VALUE 1 ASLB the body of the macro ROLA replaces the call ASLB ROLA ASLB ROLA ASLB ROLA STD RESULT You should note that a macro call differs from a Subroutine call in that the macro call results in lines of code being placed in line in the program where a subroutine call results in the execution of the routine at run time Five calls to a subroutine still only requires one copy of the subroutine while five calls to a macro results in five copies of the macro body being inserted into the program 52 FLEX 6809 Relocating Assembler Parameter Substitution If macros were limited to what was described above they would probably not be worth the space it took to implement them in the assembler The real power of macros comes in parameter substitution By that we mean the ability to pass parameters into the macro body from the calling line In this manner each expansion of a macro can be different As an example suppose we wanted to add three 16 bit numbers found in memory and store the result in another memory loca
34. d TEST 1000 like this SEX LABEL The expanded source code would look like this LDA 1000 comment field is here LDB L1000 NOP parameters can even be NOP substituted into NOP comments like this SEX or they can be a mnemonic LABEL TST M1000M or label or inside a string 57 FLEX 6809 Relocating Assembler Note that in the LDA instruction the parameter 1000 is used as a number but in the LDB and TST instructions it is part of a label The second parameter is not even substituted into the actual program but rather into the comment field The use of parameter number one in the TST instructions shows that the dummy parameter does not have to be a stand alone item but can be anywhere in the line Another convenient method of using macros is in conjunction with the IF SKIP type of conditional directive With a negative or backward skip we can cause a macro to loop back on itself during expansion A good example of this would be a case where the programmer must initialize one hundred consecutive memory locations to the numbers one through one hundred This would be a very tedious task if all these numbers had to be setup by FCB directives Instead we can use a Single FCB directive the IF SKIP type of directive and the SET directive to accomplish this task INIT MACRO COUNT SET 0 initialize counter COUNT SET COUNT 1 bump by one FCB COUNT set the memory byte IF COUNTd 2 ENDM If you try this macro out you will see that
35. d a manual describing the 6809 instruction set and addressing modes in full The former can be acquired through any of a large number of books available on assembly programming the latter from the 6809 hardware manufacturer or seller Throughout the manual a couple of notational conventions are used which are explained here The first is the use of angle brackets and These are often used to enclose the description of a particular item This item might be anything from a filename to a macro parameter It is enclosed in angle brackets to show that it is a single item even though the description may require several words The second notation is the use of square brackets and These are used to enclose an optional item Absolute Assemblers An absolute assembler such as the FLEX ASMB produces absolute machine code in which all addresses will be correct only if the program is loaded at the specified locations For example a program ORG ed at 1000 contains a JMP instruction At execution time control will be transfered to the intended location by the JMP statement only if the program resides at 1000 FLEX is a trademark of Technical Systems Consultants Inc FLEX 6809 Relocating Assembler Consider the following program KKK K cntchar count the number of characters in a null terminated string exit b count of the characters 1000 ORG 1000 1000 8E 100D CNTCHAR LDX STRING GET ADDR OF STRING 1003
36. d is equal to the address of the current instruction In a relocatable module the value of the PC designator is relocatable its value is given at loading time TYPES OF EXPRESSIONS There are three types of expressions possible in the FLEX Relocating Assembler These include absolute relocatable and external expressions a Absolute Expressions An expression is absolute if its value is unaffected by program relocation or the module is considered absolute by the presence of an ABS and ORG directive An expression can be absolute even though it contains relocatable symbols under both of the following conditions 1 The expression contains an even number of relocatable elements 2 The relocatable elements must cancel each other That is each relocatable element or multiple must be canceled by another relocatable element or multiple In other words pairs of relocatable elements must have signs that oppose each other The elements that form a pair need not be contiguous in the expression For example rell and rel2 are two relocatable symbols in a module the following examples are absolute expressions rell rel2 5 rell rel2 rel1 3 50 4 rel2 4 b Relocatable Expressions An expression is relocatable if its value is affected by program relocation in a relocatable module A relocatable expression consists of a single relocatable symbol or under all three following conditions a combination of relocatable and absolute
37. ds is termed relocation Because any code can be considered relocatable one can take advantage of the speed and space savings of absolute code with the adjustment of the address fields deferred until load time To illustrate how the Relocating Assembler and Linking Loader work in conjunction with each other we will present another version of CNTCHAR Note that it does not contain any ORG statements and that the code starts at location 0 FLEX 6809 Relocating Assembler KKKK cntchar count the number of characters in a null terminated string ai exit b count of the characters 0000 8E 000D CNTCHAR LDX STRING GET ADDR OF STRING 0003 5F CLRB SET COUNT TO ZERO 0004 A6 80 LOOP LDA 0 X GET A CHARACTER 0006 27 04 BEQ DONE IF END OF STRING 0008 5C INCB COUNT THE CHARACTER 0009 7E 0004 JMP LOOP GET NEXT CHARACTER 000C 39 DONE RTS RETURN 000D 48 4F 57 20 STRING FCC HOW MANY CHARS 0 A plus sign in front of an instruction indicates that the address field of that instruction must be increased by a relocation constant The relocation constant is the address at which the program is loaded for execution For example if the above program was loaded at 1000 the two relocatable address fields marked by must each be increased by 1000 in order for the program to execute as intended The address referred to by the first instruction would be 000D 1000 100D which would now correctly point to STRING Address fields
38. e format which means there may be any number of spaces separating each field In general no spaces are allowed within a field LABEL OR SYMBOL FIELD This field may contain a symbolic label or name which is assigned the instruction s address and may be called upon throughout the source program a Ordinary Labels 1 The label must begin in column one and must be unique Labels are optional If the label is to be omitted the first character of the line must be a space 2 A label may consist of letters A Z or a z numbers 0 9 or an underscore _ or 5F hex Note that upper and lower case letters are not considered equivalent Thus ABC is a different label from Abc 3 Every label must begin with a letter or underscore 4 Labels may be of any length but only the first 8 characters are significant 5 The label field must be terminated by a space or a return b Local Labels 1 Local labels follow many of the same rules as ordinary labels They must begin in column one and they must be terminated by a space or a return 2 Local labels are comprised of a number from 0 to 99 These numbers may be repeated as often as desired in the Same source module they need not be in numerical order 3 Local labels may be treated as ordinary labels however they cannot be global or external They may not be used in the label field of an equ or set directive 4 Local labels are referenced by using the local label number ter
39. e inserted in a powered up system you are ready to begin The Command Line The very minimum command line necessary to execute an assembly is as follows RELASMB lt fi ename gt The three plus signs are FLEX s ready prompt RELASMB is the name of the relocating assembler file it has a CMD extension and the lt filename gt is the standard FLEX specification for the source file you wish to assemble The lt filename gt defaults to a TXT extension and to the assigned working drive if an explicit extension and drive number are not given In this and forthcoming example command lines a comma is used to separate items It is also possible to use a space or spaces in this capacity As stated this is the very minimum command which can be used It is possible to supply many more parameters or options to the assembler but if left off as in this example the assembler will assume default parameters Perhaps the most important options available are the two associated with output We say two because there are two types of output available from the assembler object code output and assembled source listing output The options regarding the assembled source listing output will be described a little later The object code can be in the form of a relocatable binary disk file or no object code output at all Since no specifications are made concerning object code output in the above example the assembler will assume the default case which is a
40. e parameters may be passed to the program These parameter are simply strings of characters that will be substituted into the source listing as it is read in by the assembler These parameters are expressed in the command line in the manner shown here RELASMB lt in file gt lt bin file gt lt options gt lt prm 1 gt lt prm 2 lt prm 3 gt The parameters are optional but must be separated from the rest of the line by the second plus sign and from each other by commas As stated these parameters are simply strings of characters The string of characters which makes up an individual command line parameter can not have spaces or commas iinbedded in it Note that if one wishes to enter a command line parameter but no options he must still place both plus Signs in the command as seen in this example command line 10 FLEX 6809 Relocating Assembler RELASMB ANYFILE PARAMETER1 PARAMETER2 For further information on command line parameters and how to specify where in the source program these parameters should be substituted see the section on Special Features Qutputting to a Hardcopy Device The assembler does not have a built in means for outputting the assembled listing to a hardcopy device This operation is however available through the facilities of FLEX To do so one must use the P command provided with FLEX This P command reads a printer driver file which you can supply to output to any hardcopy device you wan
41. e statements Absolute or relocatable expressions are allowed external expressions are illegal If the expression is relocatable both the value and relocatable attribute will be assigned to the label SET The SET directive is used to set a symbol to the value of some expression much as an EQU directive The difference is that a symbol may be SET several times within the source to different values while a symbol may be Equated only once If a symbol is SET to several values within the source the current value of the symbol will be the value last SET The statement form is lt label gt SET lt non external expression gt The label is strictly required and no code is generated 38 FLEX 6809 Relocating Assembler REG The REG directive allows the user to setup a list of registers for use by the push and pull instructions This list is represented by a value and the value is equated to the label supplied In this respect the REG directive is similar to the EQU directive The correct form of the REG directive is lt label gt REG lt register list gt As an example suppose a program has a large number of occurances of the following instructions To make things more convenient and less error prone the REG directive could be used as shown here RLIST2 REG A B Y U DP Now all the pushes and pulls referred to above could be accomplished with the statements PSHS RLIST2 PULS RLIST2 Of course the register list may sti
42. ect until an ENDDEF directive is encountered For example DEFINE TEMP 1 FDB 0 FFFF START LDX 1 ENDDEF This example simply defines the two labels TEMP1 and START as global This directive works well when many symbols must be declared as global while they are initialized to various values EXT The EXT directive declares symbols to be external to this particular module Macros and local labels cannot be declared external The syntax of the EXT directive is EXT lt labell gt lt label2 gt Where labell label2 etc is an ordinary label as in GLOBAL each label should be separated by a comma When the assembler comes across a label declared external in the operand field external records will be written out to the binary output module As with the GLOBAL directive the EXT directive should appear before the actual use of the external symbol usually at the beginning of the source module These external records will be used by the linking loader 43 FLEX 6809 Relocating Assembler AME Each binary output module can be given a module name with the NAME directive The module name is used by the linking loader in reporting errors and address information it is strongly recommended to give each module a name The syntax of the NAME directive is NAME lt name of the module gt The name of the module can be a maximum of 8 characters If more than one NAME directive occurs in the source module the last name giv
43. ective excluding leading spaces is printed as an error message it will be preceded by three asterisks in the output listing Note that the ERR directive line itself is not printed A common use for the ERR directive is in conjunction with conditional assembly such that some user defined illegal condition may be reported as an error RP The RPT or Repeat directive causes the succeeding line of source to be repeated some specified number of times The syntax is as follows RPT lt absolute count gt where lt count gt may be any number from 1 to 127 For example the following two lines 41 FLEX 6809 Relocating Assembler RPT 4 ASLB would produce an assembled output of ASLB ASLB ASLB ASLB Some directives such as IF or MACRO may not be repeated with the RPT command These cases are where it is illogical or impractical to do so If attempted the RPT will simply be ignored LIB The LIB or library directive allows the user to specify an external file for inclusion in the assembled source output Under normal conditions the assembler reads all input from the file specified on the calling line The LIB directive allows the user to temporarily obtain the source lines from some other file When all the lines in that external file have been read and assembled the assembler resumes reading of the original source file The proper syntax is LIB lt file spec gt where lt file spec gt is a standard FLEX file specific
44. ed within the body of a macro Any use of it outside a macro will result in an error Macros are defined in the next section As before the possible directives are IF IFN IFC and IFNC This type of conditional assembly is performed with a single instruction Instead of code being assembled on a true result the specified number of lines are SKIPPED This number of lines can be in a forward or reverse direction The syntax is as shown IF lt absolute expression gt lt skip count gt or IFC lt string 1 gt lt string 2 gt lt skip count gt The skip count must be a decimal number between 1 and 255 It may be preceded by a plus or minus sign A positive number produces a forward skip while a negative number produces a backwards skip A skip count of zero has no effect the instruction following the IF directive will be executed next A skip count of one will cause the second line after the IF statement to be the next one executed the one line directly following the IF statement is ignored A skip count of negative one will cause the line just before the skip count to be the next one executed The assembler will not skip past the end or beginning of the macro which contains the IF SKIP statement If a skip count is specified which is beyond these limits the assembler will be left pointing to the last statement in the macro or the first depending on whether the skip count was positive or negative There can be no spaces before or after t
45. en will be the name given to the module COMMON and ENDCOM It is possible to establish common blocks in the relocating assembler These can only be named and uninitialized common blocks lt name gt COMMON A common block declaration is terminated by the use of the ENDCOM directive The only directive allowed between the COMMON and ENDCOM is RMB The RMB directives define the size of the common block labels may be associated with each RMB within the common block For example TEST COMMON TEMP1 RMB 10 TEMP2 RMB 5 ENDCOM This common block named TEST has two variables TEMP and TEMP2 associated with it and is of length 15 bytes A common block and its variables are considered external by the assembler Only one common block of a particular name should appear in a module however up to 127 common blocks of different names may occur in a module As common blocks are treated as externals the linking loader handles the resolution of references to the common blocks automatically For example TEST COMMON TEMP1 RMB 10 TEMP2 RMB 5 ENDCOM START LDD TEMP1 44 FLEX 6809 Relocating Assembler Common blocks are very useful for passing parameters and keeping common information around Furthermore the common block will have the name of the common block as its module name this is done automatically by the assembler Common blocks must be accompanied by executable code in the same module that is a common block cannot be t
46. ent SOURCE FORM COMA COMB COM Q 6800 ALTERNATES COM A COM B Clear and wait for interrupt SOURCE FORM CWAI dd Decimal adjust accumulator A SOURCE FORM DAA Decrement SOURCE FORM DECA DECB DEC 6800 ALTERNATES DEC A DEC B 29 FLEX 6809 Relocating Assembler EOR EXG INC JMP JSR LD LEA LSL LSR MUL NEG NOP OR Exclusive OR SOURCE FORM EORA P EORB P 6800 ALTERNATES EOR A P EOR B P Exchange registers SOURCE FORM EXG R1 R2 Increment SOURCE FORM INCA INCB INC Q 6800 ALTERNATES INC A INC B Jump to address SOURCE FORM JMP dddd Jump to subroutine at address SOURCE FORM JSR dddd Load register from memory SOURCE FORM LDA P LDB P LDD P LDX P LDY P LDU P LDS P 6800 ALTERNATES LDAA P LDAB P LDA A P LDA B P Load effective address SOURCE FORM LEAX T LEAY T LEAU T LEAS T Logical shift left SOURCE FORM LSLA LSLB LSL Q Logical shift right SOURCE FORM LSRA LSRB LSR Q 6800 ALTERNATES LSR A LSR B Multiply accumulators SOURCE FORM MUL Negate Two s complement SOURCE FORM NEGA NEGB NEG 6800 ALTERNATES NEG A NEG B No operation SOURCE FORM NOP Inclusive OR into register SOURCE FORM ORA P ORB P 6800 ALTERNATES ORAA P ORAB P ORA A P ORA B P 30 ORCC PSHS PSHU PULS PULU ROL ROR RTI RTS SBC SEX ST SUB FLEX 6809 Relocati
47. er object code relocation records and external records and produce executable object code Linking loaders therefore can perform the following tasks 1 load a relocatable object code module into memory 2 relocate any relative address fields 3 resolve any external references and 4 optionally execute the resultant program At this time a few definitions would be in order A global symbol is a location within a module that can be referenced from other separate modules Each global symbol has a unique name associated with it The linking loader is given a list of the global symbols in each module An external reference is a reference in one object module to a global symbol in another object module And finally a common block is a block that can be declared by more than one object module The data used in the common blocks is common to all of the modules that have declared the common block FLEX 6809 Relocating Assembler II GETTING THE SYSTEM STARTED The FLEX 6809 Relocating Mnemonic Assembler is very simple to use There are no built in editing functions you must have a previously edited source file on disk before using the assembler This file must be a standard FLEX text file which is simply textual lines terminated by a carriage return There should be no line numbers or control characters except for the carriage returns in the file When you have both the assembler and the edited source file on a disk or disks which ar
48. essages are enabled To specify which number base is desired the programmer must supply a prefix character to a number as detailed below BASE PREFIX CHARACTERS ALLOWED Decimal none 0 thru 9 Binary 0 or l Octal 0 thru 7 Hexadecimal 0 thru 9 A thru F If no prefix is assigned the assembler assumes the number to be decimal 2 ASCII CONSTANTS The binary equivalent of a single ASCII printable character may be supplied to the assembler by preceding it with a single quote The character should be between 20 and 7F hex The binary equivalent of two ASCII printable characters the first in the upper 8 bits and the second in the lower 8 bits may be supplied by preceding the two characters with a double quote 3 LABELS Labels which have been assigned some address constant relocatable or external value may be used in expressions As described above under the label field a label is comprised of letters digits and underscores beginning with a letter The label may be of any length but only the first 8 characters are significant Any label used in the operand field must be defined elsewhere in the program Local labels may also be used in the operand field None of the standard 6809 register specifications should be used as a label 4 PC DESIGNATOR The asterisk has been set aside as a ol hes FLEX 6809 Relocating Assembler special PC designator Program Counter It may be used in an expression just as any other value an
49. ession gt where the absolute expression can be any value from 1 to 65 535 This directive does produce object code FCB The FCB or Form Constant Byte directive is used to set associated memory bytes to some value as determined by the operand FCB may be used to set any number of bytes as shown below lt label gt FCB lt expr 1 gt lt expr 2 gt lt expr n gt Where lt expr x gt stands for some absolute relocatable or external expression Each expression given separated by commas is evaluated to 8 bits and the resulting quantities are stored in successive memory locations The label is optional FDB The FDB or Form Double Byte directive is used to setup 16 bit quantities in memory It is exactly like the FCB directive except that 16 bit quantities are evaluated and stored in memory for each expression given The form of the statement is lt label gt FDB lt expr 1 gt lt expr 2 gt lt expr n gt Again the label field is optional FCC The FCC or Form Constant Character directive allows the programmer to specify a string of ASCII characters delimited by some non alphanumeric character such as a single quote All the characters in the string will be converted to their respective ASCII values and stored in memory one byte per character Some valid examples follow LABEL FCC THIS IS AN FCC STRING LABEL2 FCC SO IS THIS FCC LABELS ARE NOT REQUIRED There is another method of using FCC which
50. eye or with an editor Possible NON FATAL error messages are as follows EXTERNAL SYMBOL NOT ALLOWED IN THIS CONTEXT EXTERNALLY DEFINED SYMBOL USED INTERNALLY GLOBAL SYMBOL NOT DEFINED IN THIS MODULE ILLEGAL CONSTANT ILLEGAL INDEXED MODE ILLEGAL LABEL ILLEGAL OPERAND ILLEGAL OPTION ILLEGAL RELOCATABLE EXPRESSION LOCAL LABEL TABLE OVERFLOW MACRO EXISTS MULTIPLY DEFINED EXTERNAL SYMBOL MULTIPLY DEFINED SYMBOL NESTED COMMON BLOCKS NOT ALLOWED NOT ALLOWED IN THIS CONTEXT ONLY ABSOLUTE SYMBOLS ALLOWED IN THIS CONTEXT ONLY ONE EXTERNAL SYMBOL ALLOWED IN THIS CONTEXT OPERAND OVERFLOW OVERFLOW PHASING ERROR DETECTED RELATIVE BRANCH TOO LONG SHORT BRANCHING TO EXTERNAL LABELS NOT ALLOWED SYMBOL TABLE OVERFLOW SYNTAX ERROR TOO MANY COMMON BLOCKS UNBALANCED CLAUSE UNDEFINED IN PASS 1 67 FLEX 6809 Relocating Assembler UNRECOGNIZABLE MNEMONIC OR MACRO UNDEFINED SYMBOL A couple of these could use some elaboration The OPERAND OVERFLOW message results from attempting to generate too much data from a single FCB FDB or FCC instruction A maximum of 256 bytes of data can be generated by a single instruction of that type An example of the OVERFLOW error is when LIB files are nested more than 12 levels deep The UNBALANCED CLAUSE message results when one directive of a clause is missing such as an ENDIF with no IF The NOT ALLOWED IN THIS CONTEXT message is generally associated with macros ie when an operation is
51. he comma which separates the skip count from the expression or from string 2 IMPORTANT NOTE In order for conditionals to function properly they must be capable of evaluation in pass one so that the same result will occur in pass two Thus if labels are used in a conditional expression they must have been defined in the source before the conditional directive is encountered 50 FLEX 6809 Relocating Assembler VII MACROS A macro is a facility for substituting a whole set of instructions and parameters in place of a single instruction or call to the macro There are always two steps to the use of macros the definition and the call In the definition we specify what set of instructions make up the body of the macro and assign a name to it This macro may then be called by name with a single assembler instruction line This single line is replaced by the body of the macro or the group of lines which were defined as the macro This replacement of the calling line with the macro body is called the macro expansion It is also possible to provide a set of parameters with the call which will be substituted into the desired areas of the macro body A simple example will assist in the understanding of macros Let us define a macro which will shift the D register left four places This is such a simple operation that it does not really require or make effective use of macros but it will suffice for learning purposes In actuality this rout
52. he following approximate formulae Let AVM MEMEND MEMBEG Then where AVM implies available memory MEMEND refers to the end of memory as in FLEX MEMBEG is the start of the RAM buffer area SYMBOL TABLE AVM 256 bytes 0 5 LOCAL MACRO MACRO MACRO LABEL LIST AVM 256 bytes 0 25 TEXT BUFFER AVM 256 bytes 0 1875 NAME TABLE AVM 256 bytes 0 03125 ACTIVATION BUFFER AVM 256 bytes 0 03125 SOURCE BUFFER AVM sum of above spaces These table sizes can be set manually by the programmer if so desired See the section on adapting to your system for details 64 FLEX 6809 Relocating Assembler Command Line Parameters In the section on using the assembler at the beginning of this manual command line parameters are discussed That section describes how to place a parameter on the command line for passing into the source but it does not elaborate on how the programmer tells the assembler where in the source to substitute those parameters If you have read the section on macros you should already understand the concept of parameter substitution If not read that section before continuing here Much as in macro parameter substitution there are 2 character symbols or dummy parameters which if placed anywhere in the source will be replaced by the parameters supplied on the command line In macros the parameters from the macro calling line were substituted into the macro body during expansion of the macro He
53. he only item in a single source module OPT The OPT or Option directive allows the user to choose from several different assembly options which are available to him These options are generally related to the format of the output listing and object code The options which may be set with this command are listed below The proper form of this instruction is OPT lt option 1 gt lt option 2 gt lt option n gt Note that any number of options may be given on one line if separated by commas No label is allowed and no spaces may be imbedded in the option list The options are set during pass two only If contradicting options are specified the last one appearing takes precedence If a particular option is not specified the default case for that option takes effect The default cases are signified below by an asterisk The allowable options are PAG enable page formatting and numbering NOP disable pagination CON print conditionally skipped code NOC suppress conditional code printing MAC print macro calling lines NOM suppress printing of macro Calls EXP print macro expansion lines NOE suppress macro expansion printing LIS print an assembled listing NOL suppress output of assembled listing denotes default option and is not part of option name 45 FLEX 6809 Relocating Assembler The last option may be used to turn parts of a program listing on or off as desired If the L command line option is specified howeve
54. his field upper and lower case may be used interchangeably 2 This field must be terminated by a space if there is an operand or by a Space or return if there is no operand OPERAND FIELD The operand provides any data or address information which may be required by the opcode This field may or may not be required depending on the opcode Operands are generally combinations of register specifications and mathematical expressions which can include constants symbols ASCII literals etc as explained later 15 FLEX 6809 Relocating Assembler 1 The operand field can contain no spaces 2 This field is terminated with a space or return 3 Any of several types of data may make up the operand register specifications numeric constants symbols ASCII literals and the special PC designator COMMENT FIELD The comment field may be used to insert comments on each line of source Comments are for the programmer s convenience only and are ignored by the assembler 1 The comment field is always optional 2 This field must be preceded by a space 3 Comments may contain any characters from SPACE hex 20 thru DELETE hex 7F 4 This field is terminated by a carriage return REGISTER SPECIFICATION Many opcodes require that the operand following them specify one or more registers EXG and TFR require two registers specified push and pull allow any number and the indexed addressing mode requires specification of the registe
55. in the assembler to automatically determine the offset from the current PC to that absolute address This mechanism is called PC Relative Addressing The value specified in a PC Relative address operand is the absolute value The assembler takes the difference between this absolute value and the current PC and generates that offset as part of the assembled code for the instruction If the module is relocatable PC Relative offsets will be calculated at assembly time Any PC Relative addressing to externals will always reserve a 16 bit address PC Relative Addressing is distinguished from normal PC Offset Indexing by the use cf PCR as the register name instead of PC 25 FLEX 6809 Relocating Assembler Example LEAX STRING PCR this instruction determines the offset between the PC and STRING and uses it as an offset for the PC register to determine the effective address Forcing Direct or Extended Addressing The 6809 assembler has a mechanism for forcing the assembler to perform either direct or extended addressing Under normal conditions the assembler will use direct addressing when possible for absolute modules and extended addressing for relocatable modules and external references To force the assembler to use extended addressing no matter what the conditions simply precede the operand with a greater than sign gt For example suppose the DP register was set to 00 this is the default on reset of the CPU and that we have
56. ine would probably be written in line or if required often written as a subroutine The first step is to define the macro This must be done BEFORE THE FIRST CALL to the macro It is good practice to define all macros early in a program The definition is initiated with a MACRO directive and terminated by an ENDM directive The definition of our example would be as follows ASLD4 MACRO ASLB ROLA ASLB ROLA ASLB ROLA ASLB ROLA ENDM The first line is the MACRO directive Note that the name of the macro is specified with this directive by placing it in the label field This macro name should follow all the rules for labels It will NOT be placed in the symbol table but rather in a macro name table Macros cannot be global or external The body of the macro follows and is simply lines of standard assembly source which shift the D register left four places The definition is terminated by the ENDM directive d5 1s FLEX 6809 Relocating Assembler When this macro definition is encountered during pass 1 the assembler will not actually assemble the source but instead copy it into a buffer for future access when the macro is called During pass 2 this definition is ignored At this point we may continue with our assembly program and when we desire to have the D register shifted left four places simply call the macro as follows LDA VALUE LDB VALUE 1 ASLD4 here is the macro call STD RESULT You can see that calling a macro
57. is a deviation from the standard Motorola definition of this directive This allows you to place certain expressions on the same line as the standard FCC delimited string The items are separated by commas and are evaluated to 8 bit results In some respects this is like the FCB directive The difference is that in the FCC directive expressions must begin with a letter number or dollar sign whereas in the FCB directive any valid expression will work For example 10101111 would be a valid 37 FLEX 6809 Relocating Assembler expression for an FCB but not for an FCC since the percent sign would look like a delimiter and the assembler would attempt to produce 8 bytes of data from the 8 ASCII characters which follow an FCC string The dollar sign is an exception to allow hex values such as 0D carriage return to be inserted along with strings Some examples follow INTRO FCC THIS STRING HAS CR amp LF D A FCC STRING 1 0 STRING 2 FCC 04 LABEL DELIMITED STRING Note that more than one delimited string may be placed on a line as in the second example EQU The EQU or Equate directive is used to equate a symbol to the expression given in the operand No code is generated by this statement Once a symbol has been equated to some value it may not be changed at a later time in the assembly The form of an equate statement is as follows lt label gt EQU lt nonexternal expression gt The label is strictly required in equat
58. ll be typed out on push and pull instructions or an immediate value with the desired bit pattern may be specified SETDP The SETDP or Set Direct Page directive allows the user to set which memory page the assembler will use for the direct page addressing mode The correct format is as follows SETDP lt absolute page value gt As an example if SETDP D0 is encountered the assembler will then use direct addressing for any address in the range of D000 to DOFF It is important to note that this directive does not actually affect the contents of the direct page register The value set is what will be used at assembly time to determine direct addressing but it is up to the user to be sure the DP register corresponds at run time If there is no lt page value gt supplied direct addressing will be disabled and all addresses will be full 16 bit values Any number of SETDP instructions may occur in a program The default value is page 0 for 6800 compatibility Direct addressing has more meaning for an absolute module 39 FLEX 6809 Relocating Assembler PAG The PAG directive causes a page eject in the output listing and prints a header at the top of the new page Note that the PAG option must have been previously selected in order for this directive to take effect It is possible to assign a new number to the new page by specifying such in the operand field If no page number is specified the next consecutive number will be u
59. minated with an F for the first forward reference found or a B for the first backward reference found Realize a backward or forward reference can never refer to the same line that it is found on For example 14 FLEX 6809 Relocating Assembler 2 BEQ 2F 2F next occurance of 2 2 LEAX 1 X both branches point here 2 BRA 2B 2B previous occurance of 2 5 Local labels should be used primarily but not necessarily exclusively for branching or jumping around some sections of code In most cases branching around a few lines of code does not warrant the use of an ordinary label When making reference to a nearby location in the program there often is no appropriate name with much significance therefore programmers have tended to use symbols like Ll L2 etc This can lead to the danger of using the same label twice Local labels have freed the programmer from the necessity of thinking of a symbolic name of a location For example BEQ 29F LEAX 1 X 29 STX 0 Y Furthermore local labels only require four bytes to store internally ordinary labels require twelve bytes each The maximum of local labels is dependent upon the available memory OPCODE FIELD This field contains the 6809 opcode mnemonic or pseudo op It specifies the operation that is to be performed The pseudo ops recognized by this assembler are described later in this manual 1 The opcode is made up of letters A Z or a z and numbers 0 9 In t
60. must be absolute expressions TL The TTL directive allows the user to specify a title for the program being assembled This title is then printed in the header at the top of each output listing page if the page option is selected If the page option is not selected this directive is ignored The proper form is TTL lt text for the title gt All the text following the TTL directive excluding leading spaces is placed in the title buffer Up to 32 characters are allowed with any 40 FLEX 6809 Relocating Assembler excess being ignored It is possible to have any number of TTL directives in a source program The latest one encountered will always be the one used for printing at the top of the following page s TIL The STTL or Subtitle directive is used to specify a subtitle to be printed just below the header at the top of an output listing page It is specified much as the TTL directive STTL lt text for the subtitle gt The subtitle may be up to 52 characters in length If the page option is not selected this directive will be ignored As with the TTL option any number of STTL directives may appear in a source program The subtitle can be disabled or turned off by an STTL command with no text following ERR The ERR directive may be used to insert user defined error messages in the output listing The error count is also bumped by one The proper form is ERR lt message to be printed gt All text past the ERR dir
61. nd two for flags and common block information This assembler uses a hashed symbol table technique which can mean that symbols are pseudo randomly scattered throughout the table This method is very fast but has one drawback the assembler is usually not able to completely fill all positions in the table Thus a symbol table full error message does not necessarily mean that every position in the table is really full It simply means the assembler was unable to put any more symbols in the table due to the hashing technique used However if the number of 12 byte slots is a prime number the hashing technique used will fill every slot in the table and examine each slot only once The larger the table the faster the hashing method will execute and accordingly the faster the assembler will run If possible it is good to have 50 more space in the symbol table than will be required to actually hold the number of symbols in a program LOCAL LABEL LIST This list contains all of the local labels sequentially encountered in the source code Local labels are entered and searched sequentially Each local label requires 4 bytes 1 byte for the representation of the local label 2 bytes for the address and 1 byte for flags This list should contain enough locations for all of the local labels used in a single source module SOURCE BUFFER This is the buffer which holds the source program to be assembled The assembler reads only one line of source code a
62. ng Assembler Inclusive OR immediate into CC SOURCE FORM ORCC dd Push registers onto system stack SOURCE FORM PSHS register list PSHS dd 6800 ALTERNATES PSHA PSHB PSH A PSH B Push registers onto user stack SOURCE FORM PSHU register list PSHU dd Pull registers from system stack SOURCE FORM PULS register list PULS dd 6800 ALTERNATES PULA PULB PUL A PUL B Pull registers from user stack SOURCE FORM PULU register list PULU dd Rotate left SOURCE FORM ROLA ROLB ROL Q 6800 ALTERNATES ROL A ROL B Rotate right SOURCE FORM RORA RORB ROR Q 6800 ALTERNATES ROR A ROR B Return from interrupt SOURCE FORM RTI Return from subroutine SOURCE FORM RTS Subtract with borrow SOURCE FORM SBCA P SBCB P 6800 ALTERNATES SBC A P SBC B P Sign extend SOURCE FORM SEX Store register into memory SOURCE FORM STA P STB P STD P STX P STY P STU P STS P 6800 ALTERNATES STAA P STAB P STA A P STA B P Subtract from register SOURCE FORM SUBA P SUBB P SUBD P 6800 ALTERNATES SUB A P SUB B P 31 FLEX 6809 Relocating Assembler SWI Software interrupt SOURCE FORM SWI SW12 Software interrupt 2 SOURCE FORM SWI2 SWI3 Software interrupt 3 SOURCE FORM SWI3 SYNC Synchronize to interrupt SOURCE FORM SYNC TFR Transfer register to register SOURCE FORM TFR R1 R2 TST Test SOURCE FORM TSTA TSTB TST 6800 ALTERNATES TST A TST B
63. nsion This probably does not seem logical and is not except when used with conditional assembly To portray the use of EXITM assume we have some macro called XYZ_ which has two parts The first part should always be expanded but the second should only be expanded in certain cases We could use EXITM and the IFNC directives to accomplish this as follows XYZ MACRO code that should always be generated IFNC amp 2 YES EXITM ENDIF code that is only sometimes generated ENDM 55 FLEX 6809 Relocating Assembler The following calls would result in the second part being expanded or producing code XYZ PARAMETER 1 YES XYZ PARAMETER 1 YES XYZ 0 YES while all of the following would result in the second part not being expanded XYZ PARAMETER 1 NO XYZ JUNK NO XYZ JUNK XYZ PRM1 PRM2 The EXITM directive itself requires no operand The DUP and ENDD Directives There is another type of assembler construct which may only be used inside of a macro called the DUP ENDD clause The assembler will duplicate the lines placed between the DUP and ENDD end dup instructions some specified number of times The proper form is DUP lt dup count gt code to be duplicated ENDD where the lt dup count gt is the number of times the code should be duplicated The lt dup count gt may be any valid expression but most be in the range of 1 to 255 decimal Note that DUP ENDD clauses may NOT be nested That is to say one DUP E
64. ogrammer to specify a page number at which to start printing of the assembled listing Complete instructions can be found in the next paragraph Specifying a Starting Page Number As mentioned in the P option above it is possible to specify a particular page number at which printing of the assembled listing should commence All output before that page is suppressed INCLUDING ERROR LINES When the specified page is hit printing begins and continues to the end of the assembly Note that it is possible to suspend or to completely terminate an assembly during output by use of the escape or escape return sequence found in FLEX The desired page number is specified along with the P option in the option list It must directly follow the P and should be a decimal number from 1 to 65 536 The page number itself must be directly followed by a _non alphanumeric character terminator such as a comma or space This implies that the P option if specified MUST BE THE LAST OPTION SPECIFIED The page number may also be followed or terminated by a plus sign as used in the following paragraph It is also important to note that the PAG mode must be selected pagination turned on in order for the P option to have any effect The PAG mode is turned on by default Command Line Parameters The assembler has a facility for passing information from the command line directly into the source program A maximum of three pieces of information or command lin
65. ol table section of the binary modules This will be useful in symbolic debugging L Suppress the assembled listing output If not specified the assembler will output each line as it is assembled in pass 2 honoring the LIS and NOL options see the OPT directive Those lines containing errors will always be printed regardless of whether or not this option is specified FLEX 6809 Relocating Assembler Enables the printing of decimal line numbers on each output line These numbers are the consecutive number of the line as read by the assembler Error lines are always output with the line number regardless of the state of this option Limit all symbols to only six characters internally Normally the assembler will allow the user to define and use symbols that contain eight characters However in some cases it may be necessary to limit the uniqueness of the symbols to only six characters to conform to the absolute assembler ASMB For example if you define a symbol TESTCASE and use it in the operand field as TESTCA since the absolute assembler ASMB only used six characters the 0 option would be necessary for assembly Suppress the symbol table output The assembler normally prints out a sorted symbol table at the end of an assembly This option suppresses that output Note that the L option will not suppress the symbol table output just the source itself Set all undefined symbols as external In some cases the user may
66. ot require an operand and there may be only one ELSE between an IF ENDIF pair It is possible to nest IF ENDIF clauses including ELSE s That is to say an IF ENDIF clause may be part of the lines of source found inside another IF ENDIF clause You must be careful however to terminate the inner clause before the outer There is another form of the conditional directive namely IFN which stands for if not This directive functions just like IF except that the sense of the test is reversed Thus the code immediately following is assembled if the result of the expression is NOT TRUE An IFN ELSE ENDIF clause appears as follows IFN lt absolute expression gt this code assembled if expression is FALSE ELSE j this code assembled if expression is TRUE ENDIF 48 FLEX 6809 Relocating Assembler The IFC ENDIF Clause Another form of conditional assembly is very similar to the IF ENDIF clause defined above but depends on a comparison of two strings for its conditionality instead of a _true false expression This type of conditional assembly is done with the IFC and IFNC directives for if compare and if not compare as well as the ELSE and ENDIF discussed above Thus for the IFC directive we have a clause like IFC lt string 1 gt lt string 2 gt this code assembled if strings are equal ELSE l this code assembled if strings are not equal ENDIF As can be seen the two strings are separated by a comma There are two t
67. r the LIS and NOL options are overridden and no listing occurs 46 FLEX 6809 Relocating Assembler VI CONDITIONAL ASSEMBLY This assembler supports conditional assembly or the ability to assemble only certain portions of your source program depending on the conditions at assembly time Conditional assembly is particularly useful in situations where you might need several versions of a program with only slight changes between versions As an example suppose we required a different version of some program for 4 different systems whose output routines varied Rather than prepare four different source listings we could prepare one which would assemble a different set of output routines depending on some variable which was set with an EQU directive near the beginning of the source Then it would only be necessary to change that one EQU statement to produce any of the four final programs This would make the software easier to maintain as besides only needing to keep track of one copy of the source if a change is required in the body of the program only one edit is required to update all versions The IF ENDIF Clause In its simplest form conditional assembly is performed with two directives IF and ENDIF The two directives are placed in the source listing in the above order with any number of lines of source between When the assembler comes across the IF statement it evaluates the expression associated with it we will disc
68. r by which indexing is to be done The following are possible register names A B CC DP X Y U S D PC The EXG and TFR instructions require two register specs separated by a comma The push and pull instructions allow any number of registers to be specified again separated by commas Indexed addressing requires one of X Y U or S as explained under the indexed addressing mode description EXPRESSIONS Many opcodes require that the operand supply further data or information in the form of an expression This expression may be one or more items combined by any of four operator types arithmetic logical relational and shift 163 FLEX 6809 Relocating Assembler Expressions are always evaluated as full 16 bit operations If the result of the operation is to be only 8 bits the assembler truncates the upper half If truncation occurs when warnings are enabled an appropriate message will be issued No spaces may be imbedded in an expression ITEM TYPES The item or items used in an expression may be any of four types as listed below These may stand alone or may be intermixed by the use of the operators 1 NUMERICAL CONSTANTS Numbers may be supplied to the assembler in any of the four number bases shown below The number given will be converted to 16 bits truncating any numbers greater than that If 8 bit numbers are required the 16 bit number will then be further truncated to 8 bits with notification of such if warning m
69. re the parameters from the command line are substituted into the source as it is read in from the disk In macros there were 10 possible parameters Here there are three possible The 2 character dummy parameters for these three are amp A amp B and amp C These correspond to the three possible command line parameters represented here RELASMB lt filename gt lt options gt lt prm A gt lt prm B gt lt prm C gt As can be seen the three parameters are separated by commas Just as in macros the dummy parameters can be ignored by placing a backslash directly in front of the ampersand Thus the following line of edited source VALUE EQU MASK amp COUNT would be read into the assembler as VALUE EQU MASK amp COUNT A quick example should help clarify the preceding descriptions The following program contains one dummy parameter amp A ROUTINE TO OUTPUT TO ONE OF TWO PORTS OPT PAG CON TTL OUTPUT ROUTINE FOR PORT amp A PAG IFN amp A 0 amp A 1 ERR NOT A VALID PORT NUMBER ELSE IF amp A 0 ACIA EQU E000 ELSE ACIA EQU E004 ENDIF ENDIF 65 FLEX 6809 Relocating Assembler OUTCH LDB ANDB BEQ STA RTS END ACIA 02 OUTCH ACIA Now if this file were assembled with a command line like RELASMB FILE BGDS 1 assuming the file is very creatively called FILE we would see the following assembled output OUTPUT ROUTINE FOR PORT 1 TSC ASSEMBLER PAGE 1 0000 F6 0003 C4
70. representing the number of the parameter on the calling line as seen above Thus any occurence of the dummy parameter amp 1 would be replaced by the first parameter found on the calling line Let s re do our ADD3 macro to demonstrate this process The definition of ADD3 now looks like this 53 FLEX 6809 Relocating Assembler ADD3 MACRO LDD amp l get first value in D ADDD amp 2 add in second value ADDD amp 3 add in third value STD amp 4 store result ENDM Now to call the macro we might use a line like ADD3 LOC1 LOC2 LOC3 RESULT When this macro was expanded the amp l would be replaced with LOCI the amp 2 would be replaced with LOC2 etc The resulting assembled code would appear as follows LDD LOC1 get first value in D ADDD LOC2 add in second value ADDD LOC3 add in third value STD RESULT store result Another call to the macro might be ADD3 ACE TWO LOC3 LOC1 which would result in the following expansion LDD ACE get first value in D ADDD TWO add in second value ADDD LOC3 add in third value STD LOC1 store result Now you should begin to see the power of macros There is actually a tenth parameter which may be passed into a macro represented by the dummy parameter 8 amp 0 It is presented on the calling line as so lt prm 0 gt MACNAM lt prm 1 gt lt prm 2 gt lt prm 3 gt lt prm 9 gt This parameter is somewhat different from the others in that it must be a string of characters that
71. ressions in absolute modules are absolute or external END The END pseudo op is used to signal the assembler that the end of the source input module has occurred This terminates whatever pass is currently being executed No label is allowed and no code is generated An expression may be given as shown below as the transfer address to be placed in a relocatable binary file It is optional and if supplied when no binary file is being produced will be ignored END lt expression gt Note that an end statement is not strictly required but is the only means of getting a transfer address appended to a binary output file and separating modules RMB The RMB or Reserve Memory Bytes directive is used to reserve areas of memory for data storage The number of bytes specified by the expression in the operand are skipped during assembly No code is produced in those memory locations and therefore the contents are undefined at run time The proper useage is shown here lt label gt RMB lt absolute expression gt The label is optional and the expression is a 16 bit quantity The RMB is treated as a RZB in relocatable modules except in common blocks ZB The RZB or Reserve Zero Bytes directive is used to initialize an area of memory with zeroes Beginning with the current PC location the number of bytes specified will be set to zero The proper syntax is 36 FLEX 6809 Relocating Assembler lt label gt RZB lt absolute expr
72. sed No label is allowed and no code is produced The PAG operator itself will not appear in the listing unless some sort of error is encountered The proper form is PAG lt absolute expression gt Where the absolute expression is optional The first page of a listing does not have the header printed on it and is considered to be page 0 The intention here is that all options title and subtitle may be setup and followed by a PAG directive to start the assembled listing at the top of page 1 without the option title or subtitle instructions being in the way SPC The SPC or Space directive causes the specified number of spaces line feeds to be inserted into the output listing The general form is SPC lt space count gt lt keep count gt The space count can be any number from 0 to 255 If the page option is selected SPC will not cause spacing past the top of a new page The lt keep count gt is optional and is the number of lines which the user wishes to keep together on a page If there are not enough lines left on the current page a page eject is performed If there are lt keep count gt lines left on the page after printing lt space count gt spaces output will continue on the current page If the page option is not selected the lt keep count gt will be ignored If no operand is given ie just the directive SPC the assembler will default to one blank line in the output listing Both the space count and keep count
73. sing in general Note that except for the Auto increment and Auto decrement modes determining the effective address has no effect on the register being used as the index Constant Offset Indexed This mode uses a two s complement offset value found in the byte or bytes following the opcode The offset is added to the contents of the specified register to produce a 16 bit effective address The offset may be represented as a number a symbol or any valid expression It can be either positive or negative and can be a full 16 bits Example LDA 0 X loads A from location pointed to by X LDA 5216 Y loads A from Y plus 5216 LDA 36 U loads A from U minus 36 LDA VAL S_ loads A from S plus VAL Accumulator Indexed In Accumulator indexing the contents of the specified accumulator A B or D are added to the specified indexing register as a two s complement value The result is the effective address Example LDA B Y loads A from B Y LDX D S loads X from D S Auto Increment The contents of the selected register are used as the effective address with no offset permitted After that effective address has been determined the selected register is incremented by one for single plus sign or two double plus sign Example LDA 0 X loads A from X then bumps X by 1 LDD Y loads D from Y then bumps Y by 2 24 FLEX 6809 Relocating Assembler 8d Auto Decrement In auto decrementing the selected register is first decremented by
74. t 2 Macros can be nested both in calls and in definitions That is one macro may call another and one macro may be defined inside another 3 Comment lines are stripped out of macros when defined to save storage space in the macro text buffer 4 Local labels are supported 5 A macro cannot call a library file That is a LIB directive cannot appear within a macro 6 No counting of parameters is done to be sure enough parameters are supplied on the calling line to satisfy all dummy parameters in the defined macro If the body of a macro contains a dummy parameter for which no parameter is supplied on the calling line the dumny parameter will be replaced with a null string or effectively removed 7 The macro name table is searched before the mnemonic table This means that a standard mnemonic or directive can be effectively redefined by replacing it with a macro of the same name 8 Once a macro has been defined it cannot be purged nor redefined 59 FLEX 6809 Relocating Assembler VIII SPECIAL FEATURES This section covers a few special features of the 6809 Relocating Assembler that don t seem to fit under any other specific category End of Assembly Information Upon termination of an assembly and before the symbol table is output four items of information may be printed the total number of errors encountered the total number of warnings encountered the total number of excessive branches or jumps encountered and
75. t It effectively switches the output of the assembler from going to the terminal to going to the printer For example P RELASMB TESTFILE would cause the assembled listing of the source file TESTFILE TXT to be output to the printer For further details of use of the P command refer to the FLEX User s Manual and Advanced Programmer s Guide EXAMPLES RELASMB TEST Assembles a file called TEST TXT on the assigned working drive and creates a binary file called TEST REL on the same drive The assembled listing is output to the terminal as is the symbol table RELASMB TEST LS Same as before except that no listing is output except for any lines with errors and no symbol table is output RELASMB O TEST 1 TEST TST FLSY Assembles a file from drive 0 called TEST TXT and produces a binary file on drive 1 called TEST TST The source file will have all lines starting with a semicolon assembled as though the semicolon did not exist No listing or symbol table is output and if a file by the name of TEST TST already resides on drive 1 it will be automatically deleted before the assembly starts 11 FLEX 6809 Relocating Assembler 1 RELASMB 0 TEST BAK BNGSO Loads the assembler itself from drive 1 and assembles a file called TEST BAK found on drive 0 No binary file is produced The assembled listing is output with line numbers turned on and multiple line generated code turned off No symbol table is printed all symbols are unique
76. t a time The assembly operation is carried out on each line individually This buffer may be any size so long as it will hold the longest line that may be encountered in the source 63 FLEX 6809 Relocating Assembler MACRO TEXT MACRO NAME BUFFER This is the buffer where macros are stored upon definition If few macros are to be used it can be very small The more macros anticipated the larger the buffer should be TABLE This is a table where macro names and locations are stored Each entry requires 12 bytes 8 for the macro name 2 for the address of the macro body in the macro text buffer and 2 for flags Again if few macros are to be defined this table can be quite small MACRO ACTIVATION BUFFER This buffer is an area where the macro processor builds an activation stack for all macros currently under execution Each time a macro is called certain information about it is placed on this stack If no parameters are supplied on the calling line an entry on the stack requires some 10 bytes Any calling line parameters will raise this amount If macros are not nested only one entry will be on the stack at a time However if one macro calls another there must be two entries on the stack and so on The minimum size of the stack necessary depends on tne amount of macro nesting done The assembler attempts to provide a general sizing of these tables for any size system in which it is run This sizing is done according to t
77. the address of the last byte of code assembled The number of errors is always printed in the following manner 0 Error s Detected The number of warnings are printed only if warnings have not been suppressed and if the number is greater than zero ie only if there was a warning 0 Error s Detected 2 Warning s Reported Excessive branches or jumps are printed after the error count and after the warning count If no warnings were reported the excessive branch jump count will be displayed after the error count 0 Error s Detected 3 Excessive BRANCH JUMP S Detected The last assembled address is printed only if the assembled output listing is turned off It is actually the last address which the assembler s program counter register was pointing to so there may not really be an assembled byte of code at this address For example if the last instruction in a program except for the END was an RMB directive the address would be the last byte reserved by that command This information is presented as follows Last Assembled Address 1055 The address is printed as a 4 digit hexadecimal value 60 FLEX 6809 Relocating Assembler Absolute Address Printer Specifying the A option on the assembler calling line causes an absolute address to be printed in the object code field of the assembled output listing for all relative branch instructions This is very convenient for debugging purposes especially when long branches are used E
78. tion A simple macro to do this we shall call it ADD3 would look like this ADD3 MACRO LDD LOC1 get first value in D ADDD LOC2 add in second value ADDD LOC3 add in third value STD RESULT store result ENDM Now let s assume we need to add three numbers like this in several places in the program but the locations from which the numbers come and are to be stored are different We need a method of passing these locations into the macro each time it is called and expanded That is the function of parameter substitution The assembler lets you place up to nine parameters on the calling line which can be substituted into the expanded macro The proper form for this is MACNAM lt prm 1 gt lt prm 2 gt lt prm 3 gt lt prm 9 gt where MACNAM is the name of the macro being called Each parameter may be one of two types a string of characters enclosed by like delimiters and a string of characters not enclosed by delimiters which contains no embedded spaces or commas The delimiter for the first type may be either a single quote or a double quote but the starting and ending deliniiter of a particular string must be the same A comma is used to separate the parameters These parameters are now passed into the macro expansion by substituting them for 2 character dummy parameters which have been placed in the macro body on definition These 2 character dummy parameters are made up of an ampersand amp followed by a single digit
79. u will probably want to use all the space between the end of the assembler itself and MEMEND 0AD0 Thus the lowest table would start just after the last byte of the assembler as found on the disk and the highest table would end at MEMEND 0AD1 4 The tables must be put into memory in the exact same order as they are listed above They must be put into contiguous memory 72 FLEX 6809 Relocating Assembler XI APPENDIX A LIST OF PRIME NUMBERS FROM 773 TO 2239 The symbol table is a large table that contains information about each symbol used in the source module Each symbol in this table is addressed by using a hash function This hash function uses the characters that make up the symbol and yield an address into the symbol table It is possible that two symbols will yield the same address in the table When this happens the second symbol is put into another slot in the table based upon its initial hash value Therefore it is possible that this table is not quite full yet the assembler will report a symbol table overflow message The hash algorithm is such that it is optimal when the table size is a prime number of slots Included is a table of prime numbers from 773 to 2239 773 787 797 809 811 821 823 827 829 839 853 857 859 863 877 881 883 887 907 911 919 929 937 941 947 953 967 971 977 983 991 997 1009 1013 1019 1021 1031 1033 1039 1049 1051 1061 1063 1069 1087 1091 1093 1097 1103 1109 1117 1123 1129 1151 1153 1163 1171 118
80. uss this expression in a moment and if the result is true assembles all the lines between the IF and ENDIF and then continues assembling the lines after the ENDIF If the result of the expression is false the assembler will skip all lines between the IF and ENDIF and resume assembly of the lines after the ENDIF The proper syntax of these directives is as follows IF lt absolute expression gt conditional code goes here ENDIF The ENDIF requires no additional information but the IF requires an absolute expression This expression is considered FALSE if the 16 bit result is equal to zero If not equal to zero the expression is considered TRUE 47 FLEX 6809 Relocating Assembler A more powerful conditional assembly construct is possible with the ELSE directive The ELSE directive may be placed between the IF and ENDIF statements Its effect is to switch the sense of the test for the lines between it and the ENDIF In effect the lines of source between the IF and ENDIF are split into two groups by the ELSE statement Those lines before the ELSE are assembled if the expression is true while those after up to the ENDIF are ignored If the expression is false the lines before the ELSE are ignored while those after it are assembled The IF ELSE ENDIF construct appears as follows IF lt absolute expression gt this code assembled if expression is true ELSE this code assembled if expression is false ENDIF The ELSE statement does n
81. wish to assemble a module that has some undefined references in it without specifying these as external symbols The U option will treat all undefined references as external references The U option should not substitute for the good programming pratice of listing all external symbols in the operand field of the EXT directive Suppress warning messages The 6809 assembler is capable of reporting a number of warning messages as well as an indicator of long jumps and branches that could be shortened This option suppresses the printing of these messages and indicators Produce cross reference information The assembler has the ability of producing an output file containing information that can be used by a cross reference program to create a cross reference listing This file will be called the name of the source input file with a REF extension and will appear on the same disk as the input source file If a cross reference file exists the user will be prompted for the file s deletion prior to assembly This option overrides the prompt for deleting an existing binary file In other words if the Y option stands for YES is specified an existing binary file of the same name as the one to be created will be automatically deleted without a prompt If this option is selected both the scratch file and cross reference file will be automatically deleted if they previously existed FLEX 6809 Relocating Assembler P lt no This option allows the pr
82. xcessive Branch or Jump Indicator A mechanism has been included in the assembler to inform the programmer when a long branch or jump could be replaced by a short branch The purpose is to allow size and speed optimization of the final code This indicator is a greater than si gn placed just before the address of the long branch or jump instruction which could be shortened The following section of code shows just how it looks 3420 B6 E004 INCH LDA E004 3423 84 01 ANDA 01 gt 3425 1027 FFF7 LBEQ INCH 3429 B6 E005 LDA E005 342C 81 20 CMPA 20 342E 24 06 BHS OUTCH gt 3430 BD 3436 JSR OUTCH gt 3433 7E 3420 JMP INCH 3436 34 04 OUTCH PSHS B These indicator flags may be suppressed by turning off warnings Auto Fielding The assembler automatically places the four fields of a source line label mnemonic operand and comment in columns in the output assembled listing This allows the programmer to edit a condensed source file without impairing the readability of the assembled listing The common method of doing this is to separate the fields by only one space when editing The assembled output places all mnemonics beginning in column 10 all opcodes beginning in column 17 and all comments beginning in column 27 assuming the previous field does not extend into the current one There are a few cases where this automatic fielding can break down such as lines with errors but these cases are rare and generally cause no problem 6
83. ypes of strings one enclosed by delimiters the other not The delimited type may use either a single quote or double quote as the delimiter This type of string is made up of all the characters after the first delimiter until the second delimiter is found The second type of string is simply a group of characters starting with a non space and containing no spaces or commas Thus if you need spaces or commas in a string you must use the delimited type of string It is possible to specify a null string by placing tvio delimiters in a row or by simply leaving the string out completely Note that there may be no spaces after string 1 and before the separating comma nor after the comma and before string 2 As with IFN the IFNC directive simply reverses the sense of the test such that code immediately following an IFNC directive would be assembled if the strings did NOT compare A common application of this type of conditional assembly is in macros defined in the next section where one or both of the strings might be a parameter passed into the macro The IF SKIP Clause The IF SKIP type of conditional assembly is a method which does not use in fact does not allow a related ENDIF or ELSE Instead the assembler is caused to skip a specified number of lines of source depending on the result of the expression or string comparison 49 FLEX 6809 Relocating Assembler IMPORTANT NOTE This type of conditional assembly is ONLY allow

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