CPU Sim 3.1-skrien
Contents
1. 6 2 Introduction to CPU Sim In the first closed lab the students are introduced to CPU Sim and are asked to step through the introductory tutorial given in the CPU Sim user s manual Then the students are asked to redo the previous prelab assignment using assembly language instead of machine language and finally run the resulting program in the CPU Sim environment After this first closed lab all assignments are open lab assignments 6 3 Optional Wombat Interpreter One option at this point is to ask the students to write a Wombat interpreter in their favorite high level language The interpreter should take as input a text file containing a Wombat machine language program in 0 s and 1 s as described above and should execute that program This project helps the students understand the Wombat better and gives them a feeling for how simulation and interpretation works 6 4 Introduction to the Wombat2 The next assignment is to write a more complicated assembly language program for the Wombat that accesses memory frequently After a discussion of the costs of accessing memory students are given the Wombat2 which is similar to the Wombat except it has an array of four general purpose registers and all machine instructions refer to those registers instead of an accumulator The students are then asked to redo the previous assignment this time minimizing memory references through efficient use of the four general purpose registers for2. gt mar C TransferRtoR divide 8 412 i jmpn B 412 Mainfmar gt mdr Ef TransferAtoR jmpz Al412 mdr acc i J TransferRtoA jump 9412 End J Increment load _ afai2 lt lt insertee L Set multiply 71412 J Test read 3000 16 Q EI Arithmetic stop oe _ gt gt delete C acc mar ace store 2 412 subtract 6412 C ace mar race write 4000 16 Ly ace mar gt ace b accimdr gt act New Delete Duplicate Fig 5 The dialog for editing machine instructions In addition to the execute sequence the user specifies a name for each machine instruction an opcode and a sequence of field lengths The sum of the field lengths is the length in bits of the instruction The first field corresponds to the opcode and the remaining fields correspond to operands of the instruction see Figure 5 for the dialog box for editing machine instructions CPU Sim also has a dialog box not shown here in which the user can specify the fetch sequence The fetch sequence is a sequence of microinstructions that CPU Sim executes at the beginning of each machine cycle Users can specify any sequence they wish but the fetch sequence usually includes microinstructions that fetch the next machine instruction place it in an instruction register increment a program counter and then decode the instruction in the instruction register 3 4 Saving and Viewing the Specification Once an architecture has been specified
3. asked to write recursive programs such as a simple factorial program to test the call and return instructions This turns out to be a quite difficult assignment if the JVM stack frames follow the layout described in Tanenbaum 1999 6 14 JVM4 The final improvement which leads to the JVM4 is the addition to the JVM3 of instructions that perform the creation of and allow access to arrays in the heap Students are asked to write a sorting routine for such an array 7 CPU SIM S LIMITATIONS It would be quite difficult to construct a simulator that engages the students in all the CS 2001 architecture knowledge areas and yet is simple enough for students to use in a CS3 class and at the same time allows students to construct and test hypothetical CPUs themselves Hence the author has intentionally left out some important architecture topics from CPU Sim including 1 floating point number representations 2 computer organization below the microcode level e g transistors and gates 3 issues concerning the speed of execution including those of pipelining parallel processing and the use of caches 4 interrupts and traps 5 operating system concepts such as virtual memory and file management 6 the linking and loading of separate assembly modules Adding features CPU Sim to address these topics would have made it significantly more complex and so in the author s view less pedagogically useful for the intended audience AC
4. copies are not made or distributed for profit or commercial advantage the copyright notice the title of the publication and its date of appear and notice is given that copying is by permission of the ACM Inc To copy otherwise to republish to post on servers or to redistribute to lists requires prior specific permission and or a fee 2001 ACM 1073 0516 01 0300 0034 5 00 ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 Pages 46 59 CPU Sim 3 1 47 each stage the students could also be given assembly language programming assignments that emphasize the advantages of the new features being added CPU Sim is a tool designed to facilitate such interactive hands on learning With CPU Sim students can design their own architectures from scratch or modify architectures given to them Students can simulate a variety of architectures including for example accumulator based register based RISC and stack based CPUs and they can run programs on them without the need for any physical hardware other than the computer on which CPU Sim is run With CPU Sim instructors can give students hands on experience with the following topics in the IEEE ACM Computing Curriculum IEEE ACM 2001 e numeric data representation and number bases representation of nonnumeric data microprogrammed realization of the CPU control unit instruction fetch decode and execution instruction types data manipulation control
5. holding intermediate results 6 5 Limitations of Wombat2 The next assignment asks the students to write a program for Wombat that reverses an arbitrarily long list of integers Such a program can easily be written for a CPU with a stack or with instructions with indirect or indexed addressing modes but the only way the Wombat2 can accomplish this task is with self modifying code This exercise not only teaches the students the limitations of a machine with no stack and only direct addressing but also provides a good starting point for a discussion of the advantages and disadvantages of self modifying code 6 6 Wombat3 For the next several assignments the students are not given any more hypothetical architectures Instead they are asked to gradually enhance the Wombat2 themselves to give it more power For example the students are asked to create the Wombat3 from the Wombat2 by adding a stack a new stack pointer register and push and pop machine instructions to the Wombat2 They are then asked to redo the previous assignment ACM Journal of Computer Documentation Vol 1 No 4 December 2001 CPU Sim 3 1 57 This program reads in an integer x and outputs 1 if x gt 0 or lifx lt 0 input read x and push it on the stack iflt less pop x and if x lt 0 then goto less iconst_l push a 1 on the stack goto end jump to the label end iconst_ l push a l on the stack output pop the l and write it out stop halt Fig
6. the user can save this specification in an XML file for later reloading into CPU Sim and editing The user can also save the machine specification in an HTML file which can be viewed with any web browser 4 WRITING AND RUNNING PROGRAMS IN CPU SIM Once a complete CPU architecture has been specified the user can write machine language or assembly language programs and run them on that CPU through simulation For writing such programs CPU Sim has a built in text editor including all the cut copy paste find replace print facilities desired of such an editor Machine language programs are written as text in the form of a sequence of 0 s and I s on each line followed optionally by comments These programs can be loaded into any specified RAM and then executed see Figure 6 for a sample machine language program ACM Journal of Computer Documentation Vol 1 No 4 December 2001 CPU Sim 3 1 53 W1 0 ram pO011000000000000 read n gt acc 1011000000001010 jump to Done if n lt 0 0101000000010000 add sum to the acc 0010000000010000 store the new sum 1001000000000000 go back amp read in next number 0001000000010000 load the final sum 0100000000000000 output the final sum 0000000000000000 stop ooooo00000000000 2 byte location where sum is stored 0000000000000000 oOoooo0o0000000000 Fig 6 A simple machine language program In assembly language an instruction is written using the name of a mach
7. 9 A simple JVM program using the stack to see by using the new features how much easier it is to reverse a list of integers 6 7 Wombat4 The next enhancement which results in the Wombat4 is to add call and return machine instructions allowing subroutine calls Then students are given assignments to write subprograms using value parameters and recursion The students typically have a little trouble with this assignment since there is still no addressing mode in the Wombat4 other than direct addressing which means that the only practical way to access the values on the stack is by popping them off first 6 8 Wombat5 The students are next directed to create Wombat5 by adding indirect stack relative and immediate addressing modes which allow the proper development and use of stack frames and allow call by address parameters in subroutine calls Students are asked to rewrite previous programs using subroutines that use and maintain stack frames They are also asked to manipulate arrays on the stack via indirect addressing Such manipulations might include finding the minimum or sorting the array 6 9 Wombat6 To make working with arrays even easier the students can then create the Wombat6 from the Wombats by adding an index register and indexed addressing mode at which point they can be told to redo the previous array manipulation assignment using indexed addressing 6 10 Wombat7 To make the Wombat6 more realistic the final st
8. CPU Sim 3 1 A Tool for Simulating Computer Architectures for Computer Organization Classes DALE SKRIEN Colby College CPU Sim 3 1 is an educational software package written in Java for use in CS3 courses CPU Sim provides students an active learning environment in which they can design modify and compare various computer architectures at the register transfer level and higher They can run assembly language or machine language programs for those architectures through simulation CPU Sim is a complete development environment including dialog boxes for designing the CPU architecture a text editor for editing assembly language programs an assembler several display windows for viewing the registers and RAMs during the execution of programs and many debugging features such as the ability to step forward or backward during execution inspecting and optionally changing the values in the registers and RAMs after each step These features and suggested uses of CPU Sim in CS3 classes are discussed Categories and Subject Descriptors C 0 Computer Systems Organization General Modeling of Computer Architecture 1 6 5 Simulation and Modeling Model Development K 3 1 Computers and Education Computer Uses in Education General Terms Design Languages Additional Key Words and Phrases Computer architecture simulator education 1 INTRODUCTION In a CS3 Computer Organization course students should not only read about various computer arch
9. I O instruction formats assembly machine language programming addressing modes main memory organization and operations The knowledge of a high level language is not a prerequisite to understanding and using CPU Sim but an appreciation of what is involved in programming with a high level language is useful The author has successfully used CPU Sim in his introductory machine organization classes since 1989 in conjunction with the text Structured Computer Organization Tanenbaum 1999 CPU Sim was not specifically designed to be used with that book but it works well with it The precursor to CPU Sim can be found in Kerridge et al 1980 CPU Sim version 1 0 13 and its uses in the classroom are discussed in Skrien et al 1991 A later version 2 2 was discussed in Skrien 1994 The current version of CPU Sim version 3 1 was written using Java 2 and the Swing package It was tested on computers running MacOS X Windows 98 NT 2000 and Linux This article discusses the features of CPU Sim 3 1 how to use it and gives some sample assignments The details of those assignments and their solutions are available from the author 2 MAIN DISPLAY OF CPU SIM When CPU Sim is started the main display window appears see Figure 1 Except for some dialog boxes and help windows all windows are internal to this main window The internal windows include those that display the contents of registers and RAMs and those that contain text such as asse
10. M Journal of Computer Documentation Vol 1 No 4 December 2001 CPU Sim 3 1 59 8 CONCLUSION CPU Sim is a CPU simulation program designed for use with CS3 courses which allows students to create or modify the architectures being studied It is an interactive learning environment in which students can create study and modify a variety of simple architectures at the register transfer level It is a fully integrated package that includes text editors for writing programs an assembler online help and many debugging tools to help the user easily modify the architectures and then write and execute programs on those architectures REFERENCES ABBATTISTA F DELL AQUILA C PIZZUTILO S AND TANGORRA F 2000 An object oriented simulator of computer microarchitectures In Proceedings of the IASTED International Conference on Modelling and Simulation Pittsburgh PA May AGREN O 1999 Teaching computer concepts using virtual machines SIGCSE Bull 31 2 84 85 IEEE Computer Society ACM Task Force 2001 Year 2001 model curricula for computing Aug lt http www computer org education cc2001 index htm gt KERRIDGE J AND WILLIS N 1980 A simulator for teaching computer architecture SIGCSE Bull 12 2 65 T SKRIEN D AND HOSACK J 1991 A multilevel simulator at the register transfer level for use in an introductory machine organization class SIGCSE Bull 23 1 347 351 SKRIEN D 1994 CPU Sim A computer simulato
11. a condition bit was set to 1 an error occurred or the user selected the Stop menu item the user can inspect the state of the machine including the contents of the registers and RAMs ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 54 D Skrien Go Step byinstr Step by Micro Backup one step Reset all C eh et Flush amp Reset lO Reset Control unit Instr add Micro acc mdr gt acc Fig 7 The debugging toolbar 5 CPU SIM S SPECIAL FEATURES Some of the strengths of CPU Sim include its display of registers and RAMs its editing and debugging aids and its help facilities all of which make it easier for the user to understand what is happening as a program is executing 5 1 Displaying Registers and RAMs The user can view the contents of the registers and RAMs though windows for example see the windows labeled Registers and RAM Main in Figure 1 The contents of the registers can be viewed and edited if desired in either decimal binary or hexadecimal A decimal value is converted to or from a binary value using 2 s complement representation The values in each RAM can also be displayed in these bases In addition the RAM values can be displayed and edited in groups of 1 to 8 bytes corresponding to the word size of the architecture being simulated Furthermore RAM windows include a column for comments associated with each word of memory which provides a way for the use
12. d see Figure 4 for the dialog for editing transfer microinstructions ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 50 D Skrien fez edit Modules Fig 4 The dialog for editing transfer microinstructions 2 Transfer operation from a register to a register in an array In addition to the register to register transfer specifications the user specifies which bits of what register contain the index of the destination register in the array 3 Transfer operation from a register in an array to a register This operation is similar to the preceding kind of microinstruction 4 Integer arithmetic operation addition subtraction multiplication division The user specifies the operation the two source registers the destination ACM Journal of Computer Documentation Vol 1 No 4 December 2001 10 11 12 13 14 15 CPU Sim 3 1 51 register and whether any condition bits should be set if overflow or carryout occurs Note that there is no floating point support in CPU Sim Logical Boolean operation The user specifies the operation and or nand nor xor not the source registers and the destination register Shift operation The user specifies the type of shift logical arithmetic or cyclical the direction of the shift left or right the amount of shift and the source and destination registers Test operation on bits of a register These microinstruc
13. ecify is memory or RAM A RAM is byte addressable and each RAM is accessible by the CPU only through memory access microinstructions which transfer data between registers and RAMs The user can specify as many RAMs as desired each with its own size For example the user may wish to create three RAMs one to hold the code one to hold the stack and one to hold the heap or the user may wish to use only one RAM to hold everything The last type of hardware component the user specifies is a condition bit see Figure 3 Condition bits are just specific bits of existing registers that can be set to 1 by microinstructions and optionally by arithmetic operations if an overflow or carry out occurs For example a typical status register with NZVC bits can be specified this way The user can also specify whether the setting of a condition bit will halt the execution of the current program 3 2 Specifying the Microinstructions Next the user creates microinstructions for manipulating the data in the registers and RAMs The microinstructions involving arithmetic operations assume that integer values are stored in 2 s complement representation There are 15 kinds of microinstruct ions that can be created 1 Transfer or copy operation between two registers The user specifies the registers the subset of consecutive bits of the source register to be copied and the subset of consecutive bits of the destination register into which the data is to be copie
14. ep in this series of assignments is to add bit operations and or xor not and shift operations to form the Wombat7 The ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 58 D Skrien students are then asked to write a program using these new operations to manipulate data stored in binary coded decimal format 6 11 JVM1 About two thirds of the way through the semester the students are given a simplified version of the Java Virtual Machine JVM so that they can get exposure to a CISC like stack based architecture This machine is almost identical to the IJVM discussed in Tanenbaum 1999 except that it contains only 24 machine instructions none of which allow the user to store values in variables and so requires all data to be stored on the stack by means of pushing and popping To get used to this new architecture the students are asked to write simple programs for the JVM1 and then to write slightly harder programs that require complex stack manipulations due to the lack of variables see Figure 9 for a simple JVM1 program 6 12 JVM2 Students are asked to create the JVM2 from the JVM1 by adding three new machine instructions which allow storing loading and incrementing local variables on the stack and then the students are asked to redo the previous assignment 6 13 JVM3 The students create JVM3 from JVM2 by adding procedure calls and returns After adding such instructions students are
15. ine instruction followed by a list of values either constants or symbols one for each field of the instruction For example an instruction to add the contents of register A 0 to A 1 might look like add AO Al where AO and A1 are equates with values 0 and 1 indicating the indices of the registers to be added see the window labeled W1 0 a in Figure for a sample assembly language program Assembly programs can also include the definition of equates the definitions and calls of macros and pseudoinstructions such as a data directive that initializes parts of memory to specified values or an include directive that inserts the contents of another file in the current program before assembly Once an assembly program has been written and saved to a file it can be assembled The CPU Sim assembler will check for errors in the code and if there are such errors it will display an error message and highlight the offending line in the assembly code If no errors occur the assembled machine code can be loaded into any specified RAM the user can initialize any of the registers to specified values and then execution of the program can begin If during execution the user s program requests input from the user a dialog box appears asking the user to type in a value If the program specifies output to the user this output appears in a dialog box Input and output can also be directed to and from text files Once the program halts because
16. itectures but should ideally have active hands on experience with such architectures Unfortunately providing this experience can be difficult due to the cost of a lab with the necessary hardware and the time for students to become proficient in the use of tools for working with the hardware For this reason many CPU simulators have been developed Abbatista et al 2000 Agren 1999 Yehezkel et al 2001 Yurcik 2001 Unfortunately most of these packages simulate only one fixed architecture We feel that students should be exposed to several computer architectures and ideally should have hands on experience with as many of them as possible and even hands on experience at designing some simple architectures With the use of a simulator that allows students such control over the simulation instructors have many more opportunities for providing valuable learning experiences For example to make programming easier for that architecture instructors could give students an architecture and a series of assignments that repeatedly ask the students to add and implement new features such as new addressing modes new machine instructions or new registers At Author s address Department of Computer Science 5841 Mayflower Hill Colby College Waterville ME 04901 email djskrien colby edu web http www cs colby edu djskrien Permission to make digital hard copy of part of this work for personal or classroom use is granted without fee provided that the
17. mbly programs Each of these inner windows and many of the menu items are discussed in later sections of this article 3 CPU SIM S DESIGN FEATURES In CPU Sim architectures are designed at the register transfer level That is the user specifies the registers main memories RAM microinstructions machine instructions and assembly language instructions for a hypothetical machine ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 48 D Skrien Ei Wombat1 This program reads in integers and adds them together until a negative number is read in Then it outputs the sum not including the last number 16 od00000000000000 i 16 oooo000000000000 Start read read n gt acc 12 000000000000 jmpn Done jump to Done if n lt 0 16 0000000000000000 add sun add sum to the acc 12 ooooooo00000 store sum store the new sum 000 jump Start go back amp read in next numbe load sum load the final sum write output the final sum stop stop data 2 0 2 byte location where sum is st Address paa ool__3000 jfreadn gt acc BOOA jump to Done ifn lt 0 5010 add sum to the acc 2010 store the new sum 9000 go back amp read in next number 1010 load the final sum 4000 output the final sum 0000 stop 0000 2 byte location where sum is stored 0000 Fig 1 CPU Sim s main display window A machi
18. ne instruction is implemented by a sequence of microinstructions called its execute sequence The user specifies the execute sequence of all machine instructions and so the user has complete control over the semantics of every instruction When CPU Sim executes a program it repeatedly executes machine cycles that consist of a fetch sequence a sequence of microinstructions specified by the user followed by the execute sequence of the machine instruction that was fetched 3 1 Specifying Hardware Components If users are building a new architecture they will need to first create the basic hardware components of the CPU One type of component is a register or register array ACM Journal of Computer Documentation Vol 1 No 4 December 2001 CPU Sim 3 1 49 fez edit Modules Type of Module RegisterArray vw Fig 2 The dialog for edited register arrays Users can create as many registers and register arrays as they wish with arbitrary widths number of bits For each register the user specifies a name and the width For each register array the user specifies a name the number of registers in the array and the width of all registers These arrays are specified through the dialog box shown in Figure 2 If an array of 16 registers is named A then CPU Sim automatically gives each individual register in the array the names A 0 A 1 A 15 Another type of hardware component that the user must sp
19. nt input or output the type of data being moved integer ASCII or Unicode and the external source or destination of the data either a dialog box for interaction with the user or a text file specified by the user for batch mode Decode operation This operation is used in the fetch sequence and causes the contents of a specified instruction register to be decoded and the decoded machine instruction to be executed End operation This operation indicates the end of the execution of the current machine instruction and tells CPU Sim to jump to the first microinstruction in the fetch sequence and so start a new machine cycle 3 3 Specifying the Machine Instructions and the Fetch Sequence The user specifies the semantics of each machine instruction by a sequence of microinstructions called its execute sequence Hence the user can create very simple instructions such as incrementing a register or very complex instructions with elaborate addressing schemes involving multiple registers and RAMs The user can create instructions that are RISC like in that they all have the same length and layout or the user can choose CISC like instructions with variable lengths and a variety of layouts ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 52 D Skrien SRN machine instructions name opcode fieldLengths load s implementation SPS pad 5412 i fira 15
20. r for use in an introductory computer organization class J Comput Higher Education 6 1 3 13 TANENBAUM A 1999 Structured Computer Organization 4 ed Prentice Hall Upper Saddle River NJ YEHEZKELL C YURCIK W AND PEARSON M 2001 Teaching computer architecture with a computer aided learning environment State of the art simulators In Proceedings of the 2001 International Conference on Simulation and Multimedia in Engineering Education Phoenix AZ Jan YURCIK W WOLFFE G AND HOLLIDAY M 2001 A survey of simulators used in computer organization architecture courses In Proceedings of the 2001 Summer Computer Simulation Conference Orlando FL July Received November 2001 accepted February 2002 ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001
21. r to indicate the contents of the word The assembler initializes this column with the comments on the end of each line of assembly code That is if a line of the assembly program is add sum add sum to the acc then the assembler and loader will put the assembled code in the RAM and put the comment in the corresponding comment column of the RAM window 5 2 Editing and Debugging CPU Sim has a debugging mode that users can enter when they wish to step through the execution of the program one machine instruction or one microinstruction at a time See Figure 7 for the toolbar that appears when users enter debugging mode After each such step the user can inspect and optionally edit the state of the machine CPU Sim can also be configured to highlight cells of RAMs whose addresses are in certain registers For example the top of the stack can be highlighted as well as the next instruction to be executed At any point when in debug mode the user can also back up one machine instruction at a time all the way back to the original state of the machine when debug mode was entered This ability to step forward and backward through the code makes pinpointing hardware or software errors almost trivial If the program gets into an infinite loop the user can choose Stop from the Execute menu and the program will be halted ACM Journal of Computer Documentation Vol 1 No 4 December 2001 CPU Sim 3 1 55 ACPU Sim Help File p
22. revious next CPU Sim Help E General Help Data Pseudoinstruction CI Menus Windows The word data signifies a pseudo instruction in aa oinar Features assembly language It provides a way for the user to insert Tm Machine specincanon specific numerical values in specific locations in the Names assembled code The pseudoinstruction has the following C Fetch s ett equence A parts B Machine Instructions Fj Hardware Modules j labeli data operands comment J Microinstructions i Cl Assembly Language C Syntax The word data and the operands must be included but the comment and the label are optional The label can be C Regular Instructions used as an operand in assembly language statements to refer to the first address of the data that is being specified The pseudoinstruction is terminated by the newline character data Statements include Statements C Macros C Eaus Fig 8 The CPU Sim help window 5 3 Getting Help Virtually the entire user manual is available online with CPU Sim In addition to a general help window see Figure 8 many dialog boxes have Help buttons that bring up the online help for that dialog box 6 SAMPLE ASSIGNMENTS USING CPU SIM A series of open and closed lab exercises using CPU Sim was created by the author to gradually introduce CS3 students to more and more complex machine architectures The
23. se exercises expose the students to an accumulator based machine a RISC like machine with regular instruction layout and arrays of general purpose registers and a stack based machine the Java Virtual Machine or JVM The lab exercises are assigned approximately once or twice a week in a 14 week semester with the first lab occurring in the second week of the semester The students are given about a week to complete each assignment The lab exercises are summarized here The complete assignments and their solutions can be obtained from the author 6 1 Introduction to Wombat1 Before learning to use CPU Sim students are given an exercise in which they are presented with a hypothetical machine the Wombat1 a simple accumulator based ACM Journal of Educational Resources in Computing Vol 1 No 4 December 2001 56 D Skrien machine with only 12 machine instructions no stack and only direct addressing and two programs for that machine written in binary machine language The first program is documented and the second is not The students are asked to modify the first program to do something slightly different and to figure out what the second machine language program does The purpose of this prelab assignment is a to get the students comfortable with the architecture of the Wombat before seeing it in the CPU Sim environment and b to get them to appreciate assembly language by having to program first in binary machine language
24. tions allow jumping to other microinstructions forward or backward within a microinstruction sequence The test microinstruction compares the value in a part of a register with a given value If the comparison succeeds then a number of successive microinstructions in the current sequence are skipped The user specifies the comparison to be used lt gt lt gt the value to be compared the register the bits of the register to be tested and the amount to jump if the test succeeds Branch operation This microinstruction is like a test microinstruction except that it is an unconditional jump The user specifies the amount to jump which can be positive or negative Increment operation The user specifies the register to be incremented the amount of the increment and whether any condition bits are to be set if overflow or carry out occurs Set operation This operation sets a specified part of a register to a specified value The user chooses the register the consecutive bits of that register that are to be set and the value Set condition bit operation This operation sets a condition bit to 0 or 1 The user chooses the condition bit and the value to which it is to be set Memory access operation The user specifies a data register an address register the RAM and the direction of data movement read or write I O operation The user specifies a buffer register to or from which data is to be moved the direction of data moveme
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