User Manual
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1. P 30 B 0302 08 PHP Now we can use the T command to step through the code After one step the current value of the status register P 30 will be pushed onto the stack and the stack pointer will decrease by 1 T A OD X 01 Y 07 S FC P 30 B 0303 38 SEC As we step through we can watch the changes in the status flags in response to the execution of each command Follow the below to see the carry zero and negative flags being set T A OD X 01 Y 07 S FC P 31 BC 0304 A2 00 LDX 00 T A 00 X 01 Y O7 S FC P 33 BZC 0306 CA DEX T A FF X 01 Y 07 S FC P B1 NBC 0307 28 PLP 13 After one last step the status register will be restored to its earlier value so the flags will return to off and the stack pointer increased by 1 Then as usual the R command will continue execution of the program and so the RTS command will return control to the assembler shell T A FF X 01 Y 07 S FD P 30 B 0309 60 RTS R 7 3 Using the Apple 1 monitor The minimonitor includes no commands for examining or altering memory Rather this func tionality is provided via the standard Apple 1 monitor by using the command to submit instruc tions to the monitor as shown in the following example A D2 X 00 Y 01 S FD P 33 BZC 0002 00 BRK 1000 101F 1000 00 00 00 00 00 00 00 00 1008 00 00 00 00 00 00 00 00 1010 00 00 00 00 00 00 00 00 1018 00 00 00 00 00 00 00 00 A D2 X 00 Y 01 S FD P 33 BZC 0002 00 BRK 1000 1 23 4 12. or a local label is redefined within a module 4 2 Mnemonics KRUSADER recognises the standard 3 character mnemonics for all legal 6502 instructions These are shown in table 2 Undocumented opcodes are not supported and the 65C02 support is discussed in section 6 The editor will not accept any line with an invalid entry in the mnemonic field Note that when the 6502 executes a BRK instruction the return address pushed onto the stack is PC 2 and so KRUSADER assembles the BRK opcode as two 00 bytes and an RTI will return to the next instruction However the disassembler will show these as consecutive BRK instructions Operation Mnemonics Load Store LDA LDX LDY STA STX STY Transfer TAX TXA TAY TYA TSX TXS Stack PHA PLA PHP PLP Logical AND EOR ORA BIT Arithmetic ADC SBC CMP CPX CPY Increment Decrement INC INX INY DEC DEX DEY Shift ASL LSR ROL ROR Jump Call JMP JSR RTS Branch BCC BCS BEQ BNE BMI BPL BVC BVS Status Flag CLC CLD CLI CLV SEC SED SEI Other BRK NOP RTI Table 2 Recognised mnenomics 4 3 Arguments Table 3 shows the argument format for each of the 6502 s addressing modes In addition nnnn can always be replaced by a label or expression and similarly nn so long as the result is a single byte Expressions are introduced in section 4 5 below A single byte may also be represented using c for a given printable chara
3. 000 00 A D2 X 00 Y 01 S FD P 33 BZC 0002 00 BRK 1000 1007 1000 01 02 03 04 00 00 00 00 A D2 X 00 Y 01 S FD P 33 BZC 0002 00 BRK 14 8 Low Level Information This section presents some low level information about how KRUSADER works and is not required for normal use of the assembler However there are many situations where this informa tion is quite important for managing source and machine code and correcting errors The most important memory locations are shown in table 8 and discussed in the following sections Address Function Zero Page Dependencies 7100 F000 Assembler entry F8 High byte of assembled code storage area 711C FO1C Assembler re entry shell F9 High byte of local global table boundary FE FF Address of source code storage area E9 EA Global symbol table address EB Number of global symbols 7304 F204 Move memory 50 51 Source location non overlapping 52 53 Destination 54 55 Bytes to move FE14 Mini monitor entry FO F4 Register storage S P Y X and A FE1E Mini monitor re entry F5 F6 Address of next instruction ROM version only 0F 11 Input buffer E0 E8 Code buffer for trace function 7BCA FACA Disassembler F5 F6 Address to disassemble from Table 8 Important function entry points and related memory locations The minimonitor ad dresses are FEO3 and FE16 in the 65C02 versi
4. At this point you will be presented with a brief message showing the version of the assembler you are running followed by the shell prompt Type N to enter a new program and enter the code shown below The column layout is important with the source organised in fields After the current line number is printed by the editor the next 6 characters are the label field then after a space there is the 3 character mnemonic field then after a space a 14 character arguments field and finally a comments field of maximum 10 characters Hitting tab or space will automatically progress you to the next field and to finish entering code hit the escape key hit return first though or you will lose the current line If you make an error typing a line hitting backspace will return you to the start of the line there is no true backspace on the Apple 1 and I have chosen not to implement the underscore as backspace hack used in the Apple 1 monitor and Apple 1 BASIC since it confuses the syntactically important column layout If you only notice an error after hitting return and need to change a line type E nnn where nnn is the line number in question it is not necessary to enter any leading zeroes If you missed a line out altogether type nnn to insert at line nnn N 000 LDA A 001 LOOP JSR FFEF 002 CLC 003 ADC 1 004 CMP Z 1 005 BNE LOOP 006 RTS 007 lt esc gt When you have finished entering the source type L to list the cod
5. F6 and this must be restored using either the monitor or the mini monitor if you wish to resume the program being monitored 7 1 Sample Mini Monitor Session This section gives a short example of a mini monitor session In order to work through this example first start the assembler and enter the following short program that includes a BRK instruction 10 FOOOR F000 A9 KRUSADER 6502 BY KEN WESSEN N 000 LDA A 001 JSR FFEF 002 SEC 003 BRK 004 JSR FFEF 005 RTS 006 Assemble it and examine the resulting code A 0300 030B D 300 0300 A9 41 LDA 41 0302 20 EF FF JSR FFEF 0305 38 SEC 0306 00 BRK 0307 00 BRK 0308 20 EF FF JSR FFEF 030B 60 RTS When this program is run it should print A set the carry flag C and then drop into the mini monitor R 300 A A 41 X FF Y 07 S FD P 21 BC 0308 20 EF FF JSR FFEF Use the A command to change the value in register A from 41 to 42 confirm the change by checking the new register display and then resume the program with the R command The program will then print a B corresponding to the new value in register A and return to the assembler shell as normal 442 A 42 X FF Y 07 S FD P 21 BC 0308 20 EF FF JSR FFEF R B Now let s enter a new program this time involving a subroutine call 11 N 000 LDA A 001 JSR SUB 002 JSR FFEF 003 RTS 004 005 SUB M 006 BRK 007 LDA P Z 008 RTS 009 A
6. S A LONG COMMENT 004 CMP Z 1 HERE ARE 005 BNE LOOP SHORT ONES 4 5 Expressions KRUSADER allows the use of 4 operators in a mnemonic s argument lt and gt for plus minus low byte and high byte respectively The plus and minus operators take a constant signed byte argument only and unlike other places where constants are employed the argument requires no preceeding The high and low byte operators are used to extract the relevant single byte from a word sized constant or label and have lower precedence than and and so are applied last of all when evaluating the expression For example if we define the symbols BYTE 12 and WORD 3456 then the following expressions are evaluated as listed below e BYTE 1 13 e WORD FF 3455 e BYTE 80 FF92 e gt WORD 34 e lt BYTE 80 92 e lt WORD 56 e WORD 1 3457 e gt WORD 10 34 e WORD 1 3455 e lt WORD 10 66 As described in section 4 1 forward references can be used in expressions involving the and operators but not in expressions involving the lt and gt operators 5Strictly speaking the space is not required but if it is absent the source formatting will be upset 4 6 Directives In addition to the 6502 mnemonics described in section 4 2 KRUSADER supports a number of directives for managing symbolic constants program structure and data Directives are entered in the mnemonic field and always consist of a period fol
7. User Manual for KRUSADER Ken s Rather Useless Symbolic Assembly Development Environment for the Replica 1 or is that Reasonably Useful You decide Ken Wessen ken wessen gmail com Version 1 3 December 24 2007 1 Introduction KRUSADER is a program written to allow assembly language development on the Replica 1 an Apple 1 clone designed by Vince Briel and described in the book Apple 1 Replica Creation Back to the Garage by Tom Owad KRUSADER includes a simple shell and editor a single pass symbolic assembler a disassembler and a simple interactive debugger and fits in just under 4K so it is small enough to fit in the 8K of Replica 1 ROM along with the monitor and Apple BASIC Although designed for the Replica 1 Apple 1 there is very little system dependent code and since full source code is provided KRUSADER can easily be adapted to any other 6502 based system However it s limitations may mean it is not an appropriate tool in many cases for example it has no concept of a file system and so would not be particularly suitable for use on an Apple II KRUSADER handles a fairly standard and expressive syntax for its assembly source code For users who are unfamiliar with the 6502 instruction set I recommend the introduction by Andrew John Jacobs at http www obelisk demon co uk 6502 On a Replica 1 KRUSADER can assemble over 200 lines of code per second and given its 32K of RAM the defaults provide space for ar
8. YN Syntax error in either a shell command or a source code line ERR MNE An illegal mnemonic code was encountered ERR ADD An illegal addressing mode was encountered ERR SYM A needed symbol was not found ERR OVF Too many symbols has lead to a symbol table overflow Table 5 KRUSADER error messages There are many reasons why an ERR ADD may occur especially if the offending line involves symbols For this reason it can be helpful to query the symbols involved using the V command see table 1 If the symbol is indeed the cause of the addressing mode error the V command will report a more useful error specifically ERR SYM if the symbol is undefined or ERR OVF if the symbol tables are full 6 65C02 Support With version 1 2 of KRUSADER optional support for the 65C02 processor has been included The 65C02 is an enhanced version of the basic 6502 chip offerring some extra operations and ad dressing modes and fixing a few problems with the original design Although these enhancements are all useful essentially the changes are a case of too little too late and frequently programmers choose to stick to pure 6502 code for portability reasons In addition 65C02s from various man ufacturers have slightly different command sets thus adding to the confusion However since the 65C02 is the CPU in nearly all Replica 1 computers it makes good sense for KRUSADER to sup port this chi
9. am ends with an RTS control is returned to the shell Otherwise re enter the shell at address 711C F01C D lt nnnn or LABEL gt Disassemble from address nnnn or continue from the last address if no argument Press any key to stop the disassembly Send the next line typed as a command to the Apple 1 Monitor Drop into the Apple 1 Monitor You can re enter the shell at address 711C F01C P lt c gt Panic This command attempts to recover lost source usually due to zero page data corruption If the first line of source starts with a label then give the first letter of that label as an argument to this command For more detail see the section on source tokenisation 8 2 Table 1 KRUSADER shell commands Note that any shell commands that use labels are dependent on the assembler s global symbol table being intact specifically the pointer information in zero page locations E9 EA and EB and the table data itself see figure 1 Optional arguments are indicated by lt gt Once any particular module has been assembled all local labels are cleared and an error is reported if any forward references involving local labels remain unresolved However any forward references to global labels that remain unresolved are simply held and will only cause an error if they are still unresolved once assembly of the entire program has been completed KRUSADER will report an error if a global label is redefined
10. at supports 65C02 commands in both the assembler and disassembler Still fits inside the 3840 free bytes of the Replica 1 ROM e KRUSADER 1 3 December 2007 Made source and disassembly listings continuous until key pressed Added command to the shell and minimonitor Bundled with the Krusader Toolkit an integrated editor terminal and emulator for the Replica 1 8http school anhb uwa edu au personalpages kwessen apple1 ktk zip 19
11. atures of KRUSADER while developing assembly language programs it is wise to avoid using these locations in your programs Replica 1 users need to beware of Apple 1 BASIC 15 High RAM Version ROM Version 7FFF FEFF KRUSADER code 7100 F000 E 70FF Forward References 7FFF 6E00 Local Symbols 7D00 6D00 7C00 Global Symbols 6500 7400 Program Source 1D00 2000 Program Target 0300 a 920 0100 0100 CC Zero Page is C izY 0000 Zero Page 0000 Figure 1 Memory map for both the high RAM and the ROM versions of KRUSADER Note that the global symbol table starts at the local global table boundary and grows downwards whereas the program source starts at the low address and grows upwards As mentioned in section 8 1 the important values are the high byte of the target memory the high byte of the local global symbol table boundary and the start of the source code storage For the RAM version the values are 03 6D 00 and 1D and for the ROM version they are 03 7C 00 and 20 After initialisation these values are stored in zero page locations F8 F9 FE and FF because it may overwrite several of these values so they need to be restored before returning to the KRUSADER shell 8 1 1 Changing Default Memory Locations For the RAM based version of KRUSADER the default values can be altered by changing the values at memory locations 7101 7105 and 7109 in the assembler code For the ROM based version the
12. cter when immediate mode is being used Whenever a word sized argument actually has a high byte of zero and the corresponding byte size addressing mode is legal the byte size mode will be used In addition some mnemonics support the absolute Y addressing mode but not the zero page Y mode In these cases a byte sized argument will be increased to word size in order to make the instruction legal Constants are always hexadecimal Addressing Mode Format Addressing Mode Format Implicit Absolute nnnn Accumulator Absolute X nnnn X Immediate nn or c Absolute Y nnnn Y Zero Page nn Indirect nnnn Zero Page X nn X Indexed Indirect nn X Zero Page Y nn Y Indirect Indexed nn Y Relative nn Table 3 Source code syntax for the 13 addressing modes of the 6502 4 4 Comments There are two ways to include comments in KRUSADER source Full line comments may be entered by typing a character as the first character in the line followed by a space Then all line space from the mnemonic field onwards can be used for comment text Alternatively the remainder of any line after the end of the argument field is also reserved for comments and in this case no special character is required to preceed their entry Comment entry is the only place where spaces are treated literally and examples of both kinds of comments are shown in the code snippet below 003 HERE I
13. de up of 4 modules each with their own starting address The assembler will output the following upon successful assembly A 0300 02FF SETUP 005 0280 0286 FWD OOB 0300 030A BACK 013 0320 032A MAIN 01B 0340 0349 This output shows the first source line number and the memory locations used by each module in the source code the first line can be ignored because no code is generated prior to the declaration of the SETUP module Hitting M will show the memory taken up by the source code in this case 2000 20E5 2300 23E5 and the value of global symbols can be queried by using the V command e g typing V MAIN will get the response 0340 This is important because it is the entry point for this program and running it by typing either R 340 or R MAIN will result in the output ABCDEFGHI JKLMNOPQRSTUVWXYZYXWVUTSRQPONML KJIHGFEDCBA Some other relevant features of this second example are the use of blank lines for layout and symbols to represent both constants e g START A and memory locations e g STEP 30 Also note the use of the local label LOOP in both the FWD and BACK modules Local labels are indicated by an initial and have module level scope only The and M commands are two directives recognised by the assembler for defining symbols and modules respectively It is not necessary to give a memory location argument to the M directive and indeed only in very special circumstances would you wish to do s
14. default values can only be altered after the program has been run and the alternative values must be entered directly into the zero page locations mentioned above before resuming KRUSADER at location F01C 6The P command is useful for restoring the default values to these zero page memory locations TThe P command will overwrite any values entered in this way 16 8 2 Source Tokenisation Scheme Any entered source is stored in a tokenised form in order to save space The tokenisation employed is quite simple because there was even less space available in the code to implement it Three special codes are employed 01 as a field terminator 00 as a line terminator and 02 00 to indicate a blank line Labels arguments and comments are stored as entered with the field terminator marking their end and mnemonics and directives are encoded as a single byte Program end is indicated by a line starting with 00 This simple scheme results in a reduction of the source code size by a factor of 2 to 3 Also provided in the KRUSADER distribution is C source code for a program that can convert more general source code formats to the required tokenised form so that they may be uploaded to the assembler However this simple program does not translate different formats for directives or addressing mode specification so if any such changes are required they must be done manually Once you have the converted source data simply launch KRUSADER as
15. e and then A to assemble it You should see the assembler output 0300 030C indicating the target memory locations used by the assembled code Any errors detected in the code will be displayed at this point and can be fixed using either the and E commands described above or the X nnn mmm command for deleting a range of lines the second argument mmm is optional Once the code has been successfully assembled run it by typing R 300 The program will run and output the string ABCDEFGHI JKLMNOPQRSTUVWXYZ 4The original is at http www chez com apple1 Applelproject and a version that fixes various bugs at http school anhb uwa edu au personalpages kwessen apple1 This version also adds the capability to em ulate a 65C02 based Replica 1 and then return to the shell because of the final RTS In order to illustrate some more advanced features of the assembler a second more complicated example is the following 000 ECHO FFEF 001 START A 002 END 72 003 STEP 30 004 005 SETUP M 280 006 LDA 1 007 STA STEP 008 LDA START 009 RTS OOA OOB FWD M 300 ooc LOOP JSR ECHO 00D CLC OOE ADC STEP OOF CMP END 010 BMI LOOP 011 RTS 012 013 BACK M 320 014 LOOP JSR ECHO 015 SEC 016 SBC STEP 017 CMP START 018 BPL LOOP 019 RTS O1A 01B MAIN M 340 01C JSR SETUP 01D JSR FWD O1EF JSR BACK O1F RTS 020 lt esc gt Again type L to list the code Typing A will assemble the code this time ma
16. f the memory moving subroutines inside the assembler as follows First work out non overlapping source and destination addresses call these srcL srcH destL and destH and then the size of memory to move sizeL and sizeH You can do this using the M command for source or watching the output of the A command for assembled code Then drop into the monitor using the command and enter 50 srcL srcH destL destH sizeL sizeH to set the parameters and 7304R F204R to do the move 8 4 Testing KRUSADER comes with a number of sample programs both in binary and hex dump formats and these are useful for verifying its correct operation The most important sample in this re gard is TestSuite asm which contains a number of modules for testing the assembler For the 65C02 version there is the pair of source files TestSuiteC asm for the pure 6502 tests and TestSuite65C02 asm for tests of the 65C02 extensions The first test of course is that the source 17 assembles without error then R MAIN will cause the program to verify its own assembled code and report any errors This test suite covers all the 6502 instructions using all their addressing modes and various formats for arguments where relevant as well as each of the available directives In addition both forward referencing and the various kinds of expressions supported by KRUSADER are tested both alone and in combination with various addressing modes A successful run of this suite
17. lowed by a single letter Each of the available directives is described in table 4 below Directive Action LABEL nnnn Define a named constant The label must be global in scope and redefinitions are ignored without error Ex pressions or a quoted character are allowed LABEL M lt nnnn gt Define a new module optionally at the specified address or else just continuing on from the previous module The label must be global in scope and redefinitions are ignored without error Expressions are not allowed lt LABEL gt B nn Store the byte sized value nn at the current PC Ex pressions or a quoted character are allowed but not for ward references lt LABEL gt W nnnn Store the word sized value nnnn at the current PC in little endian byte order Expressions are allowed but not forward references lt LABEL gt S cc c Store the string literal at the current PC The string must be 13 characters or less and may not containt spaces Table 4 Directives supported by KRUSADER Optional fields are indicated by lt gt 5 Errors Error reporting in KRUSADER is necessarily limited by its size constraints but nevertheless it attempts to capture as many errors and ambiguities as possible and report them in a meaningful way Errors can arise in response to a shell command or as a result of an assembly When appropriate the offending line or symbol will be displayed Error Meaning ERR S
18. may be used prior to being defined i e as forward references and up to 85 forward references are allowed However forward references are more limited than normal labels since they are always treated as words i e 2 bytes in size and any expression involving them must also result in a 2 byte value In particular this means forward references cannot be used with the lt and gt operators see section 4 5 Command Arguments Action N Start a new program This command will clear any ex isting source and prompt for source entry from line 000 lt nnn gt Insert code from line nnn or at the end if no argument If k lines are inserted existing lines from nnn are shifted down by k L lt nnn gt List the source starting from line nnn or the beginning if no argument Press any key to stop the listing xX nnn lt mmm gt Delete from lines nnn to mmm inclusive If just one argument delete line nnn only Care must be taken since this will change the line number associated with all subsequent source lines Delete cannot be undone E nnn Edit line nnn and insert after This is equivalent to typ ing X nnn followed by I nnn so the existing line is deleted immediately and as for the X command it cannot be recovered M Show the memory range used to store the current source code A Assemble the current source code V LABEL Show the value of the given label or expression R nnnn or LABEL Run from address nnnn If the progr
19. nd next instruction are displayed as follows A 41 X FF Y 07 S FD P 23 CZ 0306 20 EF FF JSR FFEF The P register is shown both as a value and as a string from NVBDIZC indicating which flags are set In the above example the zero flag Z and the carry flag C are set The prompt indicates that the mini monitor is waiting for a command Valid commands are shown in table 7 and are used to change the register values set the next instruction location or drop into the Apple 1 monitor Command Action Ann Put the value nn into the A register Xnn Put the value nn into the X register Ynn Put the value nn into the Y register Snn Put the value nn into the S register Pnn Put the value nn into the P register Lnn Set the low byte of the PC for the next instruction to be executed to the value nn Hnn Set the high byte of the PC for the next instruction to be executed to the value nn R Resume execution at the currently displayed instruction Enter the Apple 1 monitor Enter an Apple 1 monitor command T Trace execution step by step 6502 version only Table 7 Mini monitor commands To return to the mini monitor from the Apple 1 monitor type FE23R or FEOAR if you are running the 65C02 version Another useful address to remember is the disassembly routine at FADO FAF8 for the 65C02 version but bear in mind that using this routine involves changing the stored PC value at locations F5 and
20. normal enter the monitor and load in the tokenised data to the source storage memory and resume The source will then be available to KRUSADER as if you had typed it in as normal However syntax and formatting errors in the source may not be well handled since the error handling is designed around the restrictions placed on source input in the usual manner Unfortunately the binary source tokenisation is incompatible between the 6502 and 65C02 versions of the assembler due to differences in the mnemonic indices and directive encoding The C command line option may be used with the tokeniser program to specify the 65C02 version binary format One useful thing to keep in mind is the N command simply clears the source program from memory by putting a 00 as the very first byte of the source storage location So if N is typed accidentally the source can be easily restored To do this manually simply enter the monitor using and change this initial byte to either 01 if there was no label or the first byte of the label and then resume KRUSADER as normal with 711CR FO1CR This process is automated by the P command You should note however that there is no way to recover source lines deleted with the X or E commands since the memory is immediately overwritten 8 3 Moving Memory If you want to copy a block of memory to another location if you are backing up source or machine code via the expansion interface for example you can make use of one o
21. o 3 Shell Commands The previous section introduced most of the available shell commands in the context of a sample interactive session Shell commands are entered in response to the prompt and are all single key commands with between zero and two arguments If the shell cannot process an entered command ERR SYN is output to indicate a syntax error Five of the thirteen shell commands are for source editing and the others are for assembling running disassembling querying symbols and source memory using the monitor and recovery Table 1 gives a summary of all commands and their syntax 4 Source Code As described in section 2 source code in KRUSADER requires strict adherence to a specific column based format The editor both assists and enforces source code entry to match this format by auto forwarding on a space and ignoring invalid keypresses In addition any non blank line must have either a valid mnemonic or directive or start with the comment character The sections below describe the source format and the legal entries for each field in detail 4 1 Labels Labels are up to 6 alphanumeric characters in length and may be either global or local in scope Local labels are defined for the current module only whereas global labels are accessible anywhere in the program Up to 256 global labels may be defined and up to 32 local labels in any one module Local labels are any labels that begin with a i e a period Labels
22. of tests is a very good indication that KRUSADER is functioning properly Because of the size of the test suite code it can not be run with the RAM version of KRUSADER without changing the start address for program source storage as described in section 8 1 1 above in order to allow enough room for the source code the assembled code and the global symbol table Specifically prior to running KRUSADER the value at address 7101 needs to be changed to 14 or if KRUSADER is already running this value of 14 can be loaded directly into the zero page address FF 18 9 Release History e KRUSADER 1 0 May 2006 First version released Target CPU is 6502 only e KRUSADER 1 1 July 2006 Fully tested version several bug fixes over version 1 0 Comes with code for a thorough automated testing of itself Various enhancements over version 1 most notably x Forward references can cross module boundaries Symbol redefinition is reported as an error x Comment only lines x Approximately 20 faster assembly This version was added to the Replica 1 SE ROM e KRUSADER 1 2 August 2006 Fixes an obscure bug in version 1 1 that prevented assembly of JMP or JSR commands targetting page zero Improved syntax checking More compact implementation saves more than 200 bytes over version 1 1 Extra space used to implement a mini monitor for interactive debugging Also available is KRUSADER 65C02 a version th
23. on and the disassembler address is FAEA 8 1 Memory Map Proper operation of the assembler requires a number of things to reside in the machine s memory There is the assembler code itself the program source code the assembled code and various symbol tables The default arrangement for both the high RAM and the ROM versions of KRUSADER are shown in figure 1 The local symbol and forward reference tables take up a fixed 1K of space with 256 bytes taken up by the locals and the remainder for the forward references The global symbol table grows downward to a maximum of 2K corresponding to 256 symbols The two most important source locations have both been mentioned already and are 7100 F000 for initial program entry and 711C F01C for returning to the shell KRUSADER also uses a number of zero page locations but mostly as an input buffer and during assembly The only locations that absolutely must be maintained are F8 F9 FE and FF These hold the high byte of the default assembled code storage location the high byte of the local global symbol table boundary and the low and high bytes of the source code storage location respectively See figure 1 for the appropriate values Additionally locations E9 EA and EB are needed if the shell is to have access to the global symbol table for various commands see table 1 and locations 0F 10 11 EO to E8 and FO to F6 are used by the mini monitor If you wish to use all the fe
24. ound 20K of tokenised source code 7K of generated code and up to 256 global symbols The KRUSADER distribution is comprised of two source files one that can assemble and disas semble 6502 code only and the another that is able to handle the expanded 65C02 instruction set see section 6 Both versions include a mini monitor for interactive debugging see section 7 In addition two binaries of each version are supplied one to be loaded in high RAM at addresses 7100 7FFF and the other that belongs in ROM from F000 FEFF Since source is provided alternative binaries are easy to produce I use the 6502 simulator by Michal Kowalski to assemble http www brielcomputers com http www applefritter com replica 3http home pacbell net michal_k the object code and test it on the Pom1 simulator and my Replica 1 Although the latest version of KRUSADER supports the 65C02 it contains only 6502 code itself and this manual will cover the 6502 features first saving a discussion of the 65C02 enhancements until section 6 Addresses quoted in this manual will be for the high RAM version of the code with the ROM version values following in brackets but these values are easily offset for any particular starting address 2 Sample Session The best way to give a quick overview of the system and its operation is to work through a couple of simple examples First thing is to load the program and once loaded run it by typing 7100R FOOOR
25. p and this section describes this support Nevertheless no 65C02 specific operations are used in the KRUSADER code itself 6 1 Additional Mnemonics The ten 65C02 instructions supported by KRUSADER are listed in table 6 Each of these is valid on all versions of the 65C02 and also on the 65C816 No other instructions are supported specifically the single bit instructions BBR BBS RMB SMB found on the Rockwell and WDC versions of the 65C02 and the STP and WAI instructions found on the Rockwell 65C02 only are not recognised Operation Mnemonics Load Store STZ Stack PHX PLX PHY PLY Logical TSB TRB Increment Decrement INA DEA Branch BRA Table 6 Additional mnenomics supported by the 65C02 version of KRUSADER 6 2 Additional Addressing Modes The 65C02 introduced two new addressing modes zero page indirect and absolute indexed indirect The KRUSADER source code syntax for these modes is shown below e Zero Page Indirect nn e Absolute Indexed Indirect nnnn X 7 The Mini Monitor The 8K of Replica 1 ROM with Integer BASIC the Monitor and KRUSADER leaves just enough space for a simple interactive debugger and this section describes the debugger included with the ROM version of KRUSADER By making the IRQBRK vector at FFFE F point to the DEBUG routine at address FE19 FEOA for the 65C02 version execution of a BRK passes control to the mini monitor and the registers a
26. ssemble it examine the resulting code and run It will break into the mini monitor on entry to the subroutine SUB A 0300 SUB 005 0309 030C D 300 0300 A9 41 LDA 41 0302 20 09 03 JSR 0309 0305 20 EF FF JSR FFEF 0308 60 RTS 0309 00 BRK 030A 00 BRK 030B A9 5A LDA 5A 030D 60 RTS R 300 A 41 X FF Y 07 S FB P 24 B 0O30B A9 5A LDA 5A When in the mini monitor unroll the stack by adjusting the value in S and set the PC to 0305 SFD A 41 X FF Y 07 S FD P 20 B 030B A9 5A LDA 5A L05 A 41 X FF Y 07 S FD P 20 B 0305 20 EF FF JSR FFEF Now resume and A will be printed rather than Z since lines 007 and 008 were never executed Since we also adjusted the stack pointer the RTS on line 003 will return control to the assembler R A 12 7 2 Tracing Assembled Code The 6502 version of KRUSADER left just enough space free in the Replica 1 ROM for imple menting a single step trace function in the mini monitor In the absence of size constraints this function can be added to the 65C02 version as well but it would need a little bit of extra code to properly handle the BRA instruction and the absolute indirect addressing mode To see how the trace function operates enter the following short program N 000 BRK 001 PHP 002 SEC 003 LDX 0 004 DEX 005 PLP 006 RTS 007 Assemble and run and it will drop into the monitor right away A 0300 0308 R 300 A OD X 01 Y 07 S FD
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