Microprocessor Based Design and operations

Microprocessor Based Desing

1. Janice Law
SHB 729
ELEG3230BTutorial 3

2. 04/10/2010ELEG3230B Tutorial 32Outline
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Recap: Flag Registers
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Programming Model
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Data Addressing Mode
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Assembly Language & Instruction Set (I) ‰
REP, REPZ, REPNZ
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CMPS, SCAS
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LOOPING
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Summary

3. 04/10/2010ELEG3230B Tutorial 33Recap –Flag registers
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6 condition flags in flag register ‰
CF (carry flag): set to 1 when the result of an addition
has a carry out of MSB.
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PF (parity flag): set to 1 if the result has an even
number of 1s
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AF (auxiliary carry flag): set to 1 if there is a carry/
borrow of bit-3
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ZF (zero flag): set to 1 if the result is zero
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SF (sign flag): equal to MSB of result
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OF (overflow flag): set to 1 if the result is out of range

4. 04/10/2010ELEG3230B Tutorial 34Recap –Flag registers
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What are the result values in Carry, Zero, Sign,
Parity, Auxiliary Carry, and Overflow flags? ‰
0110 1001 + 0001 1001
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0111 1111 + 1000 0001
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0101 1011 + 1101 0010
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45E9h + 546Ah

5. 04/10/2010ELEG3230B Tutorial 35Programming Model

6. 04/10/2010ELEG3230B Tutorial 36Programming Model –Registers
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General Registers ‰
General use (like variables)
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Special purpose
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AX: stores the result of arithmetic and logic
instructions
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BX: stores the base (offset) address in XLAT
instruction
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CX: stores the loop count for instruction
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DX: stores the most significant part of the result in
16-bit multiplication

7. 04/10/2010ELEG3230B Tutorial 37Programming Model –Registers
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Pointer and Index Registers ‰
SP, BP, SI, DI usually store offset addresses
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SP: Stack Pointer
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BP: Base Pointer
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DI: Destination Index
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SI: Source Index
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IP usually stores offset address of the next instruction

8. 04/10/2010ELEG3230B Tutorial 38Programming Model –Registers „
Segment Registers ‰
Stores the initial address information of the
corresponding memory segments
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CS: Code Segment
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DS: Data Segment
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SS: Stack Segment
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ES: Extra Segment

9. 04/10/2010ELEG3230B Tutorial 39Programming Model –Segment and Offset
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20-bit address in memory:
16-bit segment address + 16-bit offset
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Calculate the physical address with
CS = 348Ah and IP = 4214h.

10. 04/10/2010ELEG3230B Tutorial 310Programming Model –Segment and Offset
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If it doesn’t state the segment, always use the
default segment register!
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Examples: ‰
MOV CL, [BP] (SS:[BP] -> CL)
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MOV CL, DS:[BP] (DS:[BP] -> CL)

11. 04/10/2010ELEG3230B Tutorial 311Programming Model –Sample Problems „
Assume
ES=6000h, CS=4000h, SS=7000h, DS=5000h,
IP=43E8h, SP=0000h, BP=9468h, SI=4C00h,
DI=7D00h, AX=4235h, BX=075Ah, CX=0004h,
DX=3302h. ‰
What is the next instruction’s physical address?
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What is the physical address of the top of the stack?
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Show the result of MOV ES:[BP], AH. Give the physical
address if a memory is affected.

12. 04/10/2010ELEG3230B Tutorial 312Data Addressing Mode „
Register: move from registers (AX, BX, AL,…)
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Immediate: move a constant value (without a [ ])
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Direct: move a content of an address (value with a [ ])
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Register Indirect: move a content of an address stored in a
register
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Based: move using base pointers (BP/BX)
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Indexed: move using index pointers (DI,SI)
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Based Indexed: move using both base and index pointers
(e.g., [BP+SI])
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String: move DS:[SI] to ES:[DI]
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Port: Communicate to I/O ports (using IN/ OUT)

13. 04/10/2010ELEG3230B Tutorial 313Data Addressing Mode (Con’t)

14. 04/10/2010ELEG3230B Tutorial 314Data Addressing Mode –Sample Problems „
State the physical address and content (if
available) of the destination for each of the
following problems. Assume
DS=3000h, ES=4000h, SS=5000h, CS=6000h,
IP=3388h, SP=0FFh, BP=2468h, SI=4000h,
DI=50DDh, AX=2345h, BX=77EEh, CX=3333h,
DX=2222h. ‰
MOV CL, 12h
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MOV [BP], DX
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MOVSB
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MOV WORD PTR [SI+2], 20h

15. 04/10/2010ELEG3230B Tutorial 315Assembly Language & Instruction Set (I) „
REP, REPZ, REPNZ ‰
Repeats an instruction and decrements the count in CX
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REP: repeats if CX is nonzero
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REPZ: repeats if CX is nonzero and zero flag is 1
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REPNZ: repeats if CX is nonzero and zero flag is 0
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Example
MOV AX, 0h
MOV BX, 1h
MOV CX, 0h
REP ADD AX, BX
What is the value of AX and BX?

16. 04/10/2010ELEG3230B Tutorial 316Assembly Language & Instruction Set (I) „
CMPS (compare string) & SCAS (scan string)
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REPZ CMPS stringA, stringB ‰
Set CX to the length of the string, compare stringAwith
stringB
stringA: 1 2 3 4 5 6 1 2 3 4 5 6
stringB: 1 2 3 4 8 6 1 2 3 4 5 6
ZF of CMP: 0 0 0 0 1 <-stop!
„
REPNZ SCAS stringA ‰
Scan stringAuntil item in accumulator is found
stringA: 1 2 3 4 5 6 1 2 3 4 5 6
AL : 5 5 5 5 5 <-stop!

17. 04/10/2010ELEG3230B Tutorial 317Assembly Language & Instruction Set (I) „
LOOPING ‰
JNZ : Conditional jump, jump not zero; if Z=0
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Example
MOV CX, 0Ah
MOV AX, 5h
LOOOP: DEC CX, 1h
AND AX, CX
JNZ LOOOP
What are the values of AX and CX?

18. 04/10/2010ELEG3230B Tutorial 318Assembly Language & Instruction Set (I) „
LOOPING ‰
LOOPNZ : Jump if both CX and Z are nonzero
„
Example
MOV CX, 0Ah
MOV AX, 5h
LOOOP: AND AX, CX
LOOPNZ LOOOP
What are the values of AX and CX?

19. 04/10/2010ELEG3230B Tutorial 319Summary „
Recap: Flag registers
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CF, PF, AF, ZF, SF, OF
„
Programming Model
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General registers, pointer and index registers,
segment registers
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Calculate physical address with segment and offset
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Data Addressing Mode
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Register, Immediate, Direct, Register Indirect, Based,
Indexed, Based Indexed, String, Port
„
Assembly Language & Instruction Set (I)
‰
REP, REPZ, REPNZ, CMPS, SCAS, LOOPING