Lab 1 – Assembly Language and Interfacing

1. Lab 1 – Assembly Language and Interfacing Start date: Week 3 Due date: Week 4

2. Agenda • Lab Objectives • Connecting to the board (review) • About the board • Assembly language structure and commands • Assembler directives • Compiling / downloading / running • D-Bug12 commands

3. Board Setup • Connect board to power supply • Connect to the PC through USB

4. Connecting • Open MiniIDE • Compiler options (terminal  options) • COM(X) • 9600 baud rate • Ensure compiler is asm12.exe in assembler tab • Terminal  connected • Ensure you have a terminal (terminal show terminal window) • Press the reset button on the board • You should see a D-Bug12 message

5. About the board • CISC – many instructions (we will only go over a few, there are many outlined in the text or in the manual) • A, B and D registers are the main registers for instructions • X and Y registers can be used for instructions or addressing

6. About the Board • D register is 16 bits • A and B are 8-bit PARTS of the D register A B D

7. About the Board • X and Y are both 16 bits • X and Y can also be used for addressing • Covered later in class when you talk about addressing modes

8. About the board • Memory • There are only certain areas in memory that you can use • These areas can be used for data or code • There are commands to load from and store to RAM

9. About the Board • Other Functionality (covered as needed in later labs) • I/O ports • A/D ports • Timers • Interrupts • Serial ports • Etc.

10. Assembly Language Structure • 4 fields • Label • Operation • Operand • Comment • startldaa#$03 ;load a reg

11. Assembly Language Structure • Label • Used to mark a certain part of the code • Useful when doing branches / jumps • Can use them almost like a GOTO • You make them up, so can be any word you want • Labels are optional, use where needed • start ldaa #$03 ;load A reg

12. Assembly Language Structure • Operation • Describes the operation you want to do • Many operations available because CISC • Ex. Add, subtract, or, load, store, branch • start ldaa #$03 ;load A reg

13. Assembly Language Structure • Operand • Describes what you want to do the operation to • Manual will tell you what operands you need with what operations • #$03 = immediate, $03 = direct • $=hex, %=binary, nothing = decimal • start ldaa #$03 ;load A reg

14. Assembly Language Structure • Comment • Start with a semi-colon for comment to end of line • Very helpful in assembly code because it can be hard to understand • start ldaa #$03 ;load A reg

15. Assembly Instructions - load LDAA, LDAB, LDD, LDX, LDY • Load a register with a value • Syntax: (label) LDAA value • LDAA #$30 = load register A with the value $30 • LDAA $30 = load register A with the value held in memory location $30

16. Assembly Instructions - store • STAA, STAB, STD, STX, STY • Store the value in a register to a memory location • Syntax: (label) STAA memory_location • STAA $30 = store the value in register A to memory location $30

17. Assembly Instructions - Add • Ex. ADDA, ADDB, ADDD, ABA • More in manual • ADDA, ADDB = add 8-bit operand to register A or B • (label) ADDA $30 = add the value in memory location $30 to A, and store in A • (label) ADDA #$30 = add the value $30 to A and store in A • ADDD = add 16-bit operand to register D • ABA = add registers A and B and store in A

18. Assembly Instructions - SWI • SWI stands for software interrupt • Use it to end your programs and to get back out to the D-Bug12 prompt • No operand

19. Compiler Directives • Compiler directives give instructions to the compiler • Reserve space, set memory locations etc. • Not actually executed like an instruction

20. Compiler Directives - org • Org is used to tell the compiler where to put the program in memory • Unlike high level languages, where the program gets put anywhere it fits, in assembly you have to tell the compiler where to start putting the program • You can have multiple orgs in a program, ex to separate space for data and for the program (try not to have too many though)

21. Compiler Directives – org con’t • There are only certain areas on the board your can use for your program/data • A memory map of the system shows where you can put your code/data • See appendix • You have from $1000 to $4000 • $1000 is good for the program because it is big • Ex. org $1000

22. Compiler Directives - RMB • RMB stands for reserve memory byte • Operand is the number of bytes to reserve • You can then use these to store data • If they are labelled you can refer to them by the label • (label) RMB 2

23. Compiler Directives - EQU • EQU = equate • Like C #define • Compiler will go through and substitute before the code is compiled • Requires a label to use • label EQU $30

24. Compiler Directives - other • BSZ = block set zero • Like RMB, but fills the blocks with 0’s • FCB = form constant byte • Stores values specified in memory • (label) FCB $30 • (label) FCB 30, $40, ‘a’ • FDB = form double byte • Same as FCB, but 16 bits • FCC = form constant character • (label) FCC ‘hello world’

25. Example org $1000 val0 RMB 1 three EQU $03 org $1100 start LDAA #three STAA val0 SWI

26. Compiling • Save as “whatever.asm” • you have to type the “.asm” part too • Press the build button • Check the output window for errors and warnings

27. Downloading and Running • To load: • Type “load” at the prompt • Click the download button • Select your s-record file (.s19) • To run • Figure out where your program starts (your probably used an ORG right before, so wherever you ORG’d to) • ex. At $1100…type “g 1100”

28. D-Bug12 commands • Once your program has exited, you can use D-Bug12 to analyze the output • Important ones: • load • g • md • mm • rd • Others in Lab 0

29. D-Bug12 commands - md • md = memory display • Md <start address> (<end address>) • Shows the contents of memory starting at the start address • Ex, you ORG’d at $1000 and then used RMB to store some data. To see it, type: md 1000

30. D-Bug12 commands - mm • To modify a memory location • mm <address> <value> • Ex, you load data from a certain memory location at 800, but you want to change it without recompiling • mm 1100 40

31. D-Bug12 commands - RD • rd = register display • Use it to see the contents of all the user registers, flags, stack points and PC • No operands, just “rd”

32. Academic Misconduct • Reports and demos are submitted as a group, but it is a SINGLE group effort • You may talk with other groups but sharing code or reports is NOT ALLOWED • Copying code/reports from previous years is also NOT ALLOWED • If we find copying we are REQUIRED to report it