Introduction to Assembly Language Programming (Instruction Set) 1/18/2011 1

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1 Introduction to Assembly Language Programming (Instruction Set) 1/18/2011 1

2 High Level Language Compiler Assembly Language Assembler Machine Code Microprocessor Hardware 1/18/2011 2

3 8085A Instruction Set Data Transfer Instruction Move data between registers or between memory locations and registers. Includes moves, loads, stores and exchanges. Arithmetic Instruction Adds, Subtracts, Increments, Decrements data in registers or memory. Logic Instruction ANDs, ORs, XORs, compares, rotates or complements data in registers or between memory and registers. 1/18/2011 3

4 Branch/Jump Instruction Initiates conditional or unconditional jumps, calls, returns and restart. Stack, I/O and Machine Control Instruction Includes instructions for maintaining stack, reading from input port, writing to output port, setting and reading interrupt mask and clearing flags. 1/18/2011 4

5 Microprocessor System Block diagram 1/18/2011 5

6 Programming Model 0000H 8 bit 0001H 0002H A FLAG 0003H B C 0004H D E 0005H H L 0006H SP PC FFFDH CPU FFFEH FFFFH 8 bit 00H 01H 02H 03H 04H 05H 06H FDH FEH FFH 8 bit 1/18/ MEMORY I/O

7 Data Transfer IMMEDIATE DATA TRANSFER Move immediate 8 bit MVI reg, data8 ;data8 (reg) Load register pair immediate LXI rp,data16 ;data16 (rp) REGISTER DATA TRANSFER Move copy from source to destination MOV reg1, reg2 ;(reg2) (reg1) reg (Register) : A,B,C,D,E,H,L rp (Register Pair): BC,DE,HL & SP 1/18/2011 7

8 Example MVI A,10 MVI B, B MVI D,7FH ;A=0AH ;B=91H ;D=7FH LXI B,3 LXI H,2345H LXI D,100 LXI SP,3FF0H ;B=00H, C=03H ;H=23H, L=45H ;D=00H, E=64H ;SPH=3FH,SPL=F0H 1/18/2011 8

9 Example MVI MOV MOV MOV MOV MOV HLT B, 55H A, B C, A H, C L, A E, L 1/18/2011 9

10 DIRECT DATA TRANSFER Load Accumulator Direct LDA address16 Store Accumulator Direct STA address16 Load H and L Register Direct LHLD address16 Store H and L Register Direct SHLD address16 1/18/

11 Example 0000H LDA 3000H (3000H) (A) STA 2100H (A) (2100H) STORE A x 1 LOAD A y H H 2101H 2102H H H x 1 y 1 1/18/

12 Example LHLD 8000H (8000H) (L) (8000H + 1) (H) SHLD 3500H (L) (3500H) L H x 1 x H 0001H STORE H 3501H 3502H.. L y H LOAD.. (H) (3500H + 1) 8001H y 2 H y H x 1 x 2 y 1 1/18/

13 INDIRECT DATA TRANSFER Load Accumulator Indirect LDAX B ;pointer is BC register LDAX D ;pointer is DE register Store Accumulator Indirect STAX B ;pointer is BC register STAX D ;pointer is DE register 1/18/

14 INDIRECT DATA TRANSFER Move copy from memory to register indirect MOV reg, M ;pointer is HL register Move copy from register to memory indirect MOV M, reg ;pointer is HL register Move copy immediate data to memory indirect MVI M, data8 ;pointer is HL register 1/18/

15 Example ORG 0000H LXI B, 2020H MVI A, 88H STAX B INX B LDAX B LXI H, 3000H MOV D, M MOV M, A B C A 88H 20H 20H D H L 30H 00H 0000H 0001H 0002H 0003H 0004H 0005H 0006H 2020H 88H 2021H AAH 3000H FFH 1/18/

16 Instruction INX increment Register pair BC = 2021H 0000H 0001H 0002H 0003H 0004H 0005H 0006H 2020H 88H B C A AAH 20H 21H 2021H AAH D FFH H L 30H 00H 3000H AAH 1/18/

17 Transfer 10 byte data from memory location 3000h to memory location 3500h using LDA & STA 0000H LDA 3000H 0001H STA 3500H H 3001H x 1 x. LDA 3009H STA 3509H H H 3509H x 10 1/18/ x 2.. x 10 x 1....

18 Transfer 10 byte data from memory location 3000h to memory location 3500h using LDAX & STAX LOOP: MVI H,10 LXI B, 3000H LXI D, 3500H LDAX B STAX D INX B INX D DCR H JNZ LOOP HLT 0000H 0001H H 3001H H 1/18/ H H x 1 x 2.. x 10 x 1.. x 10

19 Arithmetic Operation ALU FLAG CPU REGISTER 1/18/

20 Arithmetic Instruction ADDITION Add immediate to Accumulator ADI data8 ;(A) + data8 (A) Add register to Accumulator ADD reg ;(A) + (reg) (A) Add immediate to Accumulator with Carry ACI data8 ;(A) + data8 + CY (A) Add register to Accumulator with Carry ADC reg ;(A) + (reg) + CY (A) Add register pair to HL register DAD rp ;(HL) + (rp) (HL) 1/18/

21 EXAMPLE ADI 99H ; A contains 88 (H) register A decimal constant decimal register A decimal S = 0 Bit D7 = 0 after addition Z = 0 The accumulator contains other than zero after addition AC = 1 There is a carry out of bit D3 to bit D4 during addition P = 1 The accumulator contains an even number of 1 s after addition CY = 1 There is an overflow as a result of the addition 1/18/

22 EXAMPLE ADC B ; A contains 88 (H) B contains 99 (H) ; CY =1 CY 1 register A register B register A Flag : S = 0, Z = 0, AC = 1, P = 1,CY = 1 1/18/

23 SUBTRACTION Subtract immediate from Accumulator SUI data8 ;(A) - data8 (A) Subtract register or memory from Accumulator SUB reg ;(A) - (reg) (A) Subtract immediate with Borrow SBI data8 ;(A) - data8 - CY (A) Subtract source and borrow from Accumulator SBB reg ;(A) - (reg) - CY (A) 1/18/

24 INCREMENT/DECREMENT Increment contents of Register/Memory by 1 INR reg ;(reg) + 1 (reg) Decrement contents of Register/Memory by 1 DCR reg ;(reg) - 1 (reg) Increment Register pair by 1 INX rp ;(rp) + 1 (rp) Decrement Register pair by 1 DCX rp ;(rp) - 1 (rp) Note : No Flag Effected for INX & DCX 1/18/

25 Logic Instruction AND AND Immediate With Accumulator ANI data8 (A) Λ Data8 (A) AND Register/Memory With Accumulator ANA reg (A) Λ (Reg) (A) 1/18/

26 OR OR Immediate With Accumulator ORI data8 (A) V Data8 (A) OR Register/Memory With Accumulator ORA reg (A) V (Reg) (A) 1/18/

27 EXCLUSIVE-OR EX-OR Immediate With Accumulator XRI data8 (A) Data8 (A) EX-OR Register/Memory With Accumulator XRA reg (A) (Reg) (A) 1/18/

28 Write an assembly language program to clear bit 7 and set bit 3 and 4 of memory location 3200h. ORG 2000H LDA 3200H ANI B ORI B STA 3200H RST 1 1/18/

29 COMPLEMENT THE ACCUMULATOR CMA ( A) (A) A COMPLEMENT THE CARRY STATUS CMC ( CY) (CY) 1/18/

30 COMPARE Compare Accumulator With Immediate Data CPI data8 (A) data8 Compare Accumulator With Register/Memory CMP reg (A) (reg) Note: Only flag affected 1/18/

31 Write an assembly program to find a largest value between two number at memory location 3000h and 3001h and store to memory location 3002h STORE: ORG 2000H LDA 3000H MOV B, A LDA 3001H CMP B JNC STORE MOV A, B STA 3002H RST 1 ;(A) (B) ;CY=0 IF (A) > (B) ;CY=1 IF (A) < (B) 1/18/

32 Rotate Rotate Accumulator Right Through Carry RAR (A 0 ) (CY) (A n+1 ) (A n ) (CY) (A 7 ) CY A7 A6 A5 A4 A3 A2 A1 A0 1/18/

33 Rotate Rotate Accumulator Left Through Carry RAL (A 7 ) (CY) (A n ) (A n+1 ) (CY) (A 0 ) CY A7 A6 A5 A4 A3 A2 A1 A0 1/18/

34 Rotate Rotate Accumulator Right RRC (A 0 ) (A 7 ) (A n+1 ) (A n ) (A 0 ) (CY) CY A7 A6 A5 A4 A3 A2 A1 A0 1/18/

35 Rotate Rotate Accumulator Left RLC (A 7 ) (A 0 ) (A n ) (A n+1 ) (A 7 ) (CY) CY A7 A6 A5 A4 A3 A2 A1 A0 1/18/

36 Branch Instruction Unconditional Jump JMP address16 (Byte 3) (Byte 2) (PC) Conditional Jump J Condition address16 If (Condition= true) (Byte 3) (Byte 2) (PC) 1/18/

37 Condition JZ Z=1 Jump if Zero flag SET JNZ Z=0 Jump if Zero flag NOT SET JC CY=1 Jump if Carry flag SET JNC CY=0 Jump if Carry flag NOT SET JM S=1 Jump if Sign flag SET JP S=0 Jump if Sign flag NOT SET JPE P=1 Jump if Parity flag SET JPO P=0 Jump if Parity flag NOT SET 1/18/

38 Example 1 Check Zero Flag LOOP: MVI B, 255 DCR B JNZ LOOP ;if Z == 0 then goto ;LOOP 1/18/

39 Example 2 Write a program based on the following algorithm. if contents of memory 2500h < 55h write 00h to 3000h if contents of memory 2500h > 55h write FFh to 3000h if contents of memory 2500h = 55h write 80h to 3000h LDA 2500H CPI 55H ;(A) 55H JNC CHK_EQUAL ;CY == 0? MVI A, 00H JMP STORE CHK_EQUAL: JZ EQUAL ;Z == 1? MVI A,FFH JMP STORE EQUAL: MVI A, 80H STORE: STA 3000H RST 1 1/18/

40 Unconditional Call Subroutine CALL address16 (PCH) ((SP) 1) (PCL) ((SP) 2) (SP) 2 (SP) (Byte 3)(Byte 2) (PC) 1/18/

41 Conditional Call Subroutine C Condition address16 If (Condition = True) (PCH) ((SP) 1) (PCL) ((SP) 2) (SP) 2 (SP) (Byte 3)(Byte 2) (PC) 1/18/

42 CZ Z=1 Call if Zero flag SET CNZ Z=0 Call if Zero flag NOT SET CC CY=1 Call if Carry flag SET CNC CY=0 Call if Carry flag NOT SET CM S=1 Call if Sign flag SET CP S=0 Call if Sign flag NOT SET CPE P=1 Call if Parity flag SET CPO P=0 Call if Parity flag NOT SET 1/18/

43 Return From Subroutine RET ((SP)) (PCL) ((SP) + 1) (PCH) (SP) + 2 (SP) 1/18/

44 Return From Subroutine (Conditional) R Condition If (Condition = True) ((SP)) (PCL) ((SP) + 1) (PCH) (SP) + 2 (SP) 1/18/

45 RZ Z=1 Return if Zero flag SET RNZ Z=0 Return if Zero flag NOT SET RC CY=1 Return if Carry flag SET RNC CY=0 Return if Carry flag NOT SET RM S=1 Return if Sign flag SET RP S=0 Return if Sign flag NOT SET RPE P=1 Return if Parity flag SET RPO P=0 Return if Parity flag NOT SET 1/18/

46 Example: Find the smallest value between memory content 2100h and 2101h and store at 2200h. Also find the smallest value between memory content 2110h and 2111h and store at 2201h LXI SP, 3FF0H ;init Stack Pointer LDA 2100H MOV B, A LDA 2101H CALL FIND_SMALL ;call subroutine STA 2200H LDA 2110H MOV B, A LDA 2111H CALL FIND_SMALL ;call subroutine STA 2201H RST 1 FIND_SMALL: CMP B ;Subroutine JC EXIT MOV A, B EXIT: RET END 1/18/

47 I/O,Stack, Machine Control Instruction Stack Operation Write The Content of Register Pair Onto The Stack PUSH rp (reg high) ((SP) 1) (reg low) ((SP) 2) (SP) 2 (SP) 1/18/

48 Write The Content of Accumulator & Flag Status Onto The Stack PUSH PSW (A) ((SP) 1) (Flag) ((SP) 2) (SP) 2 (SP) 1/18/

49 Retreive The Content of Register Pair From The Stack POP rp ((SP)) (reg low) ((SP) + 1) (reg high) (SP) + 2 (SP) 1/18/

50 Retreive The Content of Accumulator & Flag Status From The Stack POP PSW ((SP)) (Flag) ((SP) + 1) (A) (SP) + 2 (SP) 1/18/

51 STACK OPERATION Lecture 2 (Revision) 1/18/

52 How the Stack Works The stack is a reserved area of memory. It operates as a last-in first-out bank of registers. The memory locations, which constitute the stack, are used to store binary information temporarily during program execution. The stack can be located anywhere in read/write memory, but is usually defined such that it neither interferes with the program memory space or the data memory space. The start address of the stack is specified at the initialisation stage of the program by loading the 16-bit CPU register, called the stack pointer, with the desired address of the start of the stack. e.g LXI SP, data 16 1/18/

53 How the Stack Works Data from CPU register pairs are stored in the stack area of memory when the processor executes a push rp instruction. The contents of the program counter is automatically stored in the stack area of memory whenever the processor executes a call or restart (rst n) instruction. Data stored in the stack area of memory are returned to processor register pairs when the processor executes a pop rp instruction. Data is automatically transferred from the stack area of memory to the program counter whenever the processor executes a return (ret) instruction. 1/18/

54 Writing to the Stack To execute the instruction push HL assuming initial sp contents is 2099 H. The stack pointer is decremented by 1 (sp=2098) and the contents of H are written to this location. The stack pointer is decremented by 1 (sp=2097) and the contents of L are written to this location. Note : When data is written to the stack the stack pointer is first decremented and then the data is written 1/18/

55 Reading from the Stack To execute the instruction pop BC assuming initial sp contents is 2097 H. The contents of the memory location at the address specified by the contents of sp is moved to register C and sp is incremented. The contents of the memory location at the address specified by the contents of sp is moved to register B and sp is incremented. Note : When data is read from the stack the data is read first and then the stack pointer incremented. 1/18/

56 Example Write a program to exchange the contents of BC register with DE register Program 1 Program 2 MOV H,B MOV L,C MOV B,D MOV C,E MOV D,H MOV E,L PUSH B PUSH D POP B POP D 1/18/

57 Input/Output Operation Input From The Port IN Port_Address (port) (A) Output To Port OUT Port_Address (A) (Port) 1/18/

58 Example Input From The Port IN 80H STA 2100H ;Read from Port 80H ;Store to Memory Output To Port MVI A, 01H OUT 81H ;Write 01H to Port 81H 1/18/

59 Example: Blink LED at Port A 8255 LXI SP, 3FF0H MVI A, 80H OUT 83H REPEAT: MVI A,0 OUT 80H CALL DELAY MVI A,1 OUT 80H CALL DELAY JMP REPEAT ;init Stack Pointer ;Init 8255, all port as output ;Call subroutine ;Call subroutine DELAY: LOOP: MVI B, 0 ;Subroutine DCR B JNZ LOOP RET END 1/18/

60 Interrupt RIM SIM DI EI Read interrupt mask Set Interrupt mask Disable Interrupt Enable Interrupt (Detail discussion in interrupt topic) 1/18/

61 NEXT WEEK ASSEMBLY LANGUAGE PROGRAMMING 1/18/

INSTRUCTION SET OF 8085

INSTRUCTION SET OF 8085 Instruction Set of 8085 An instruction is a binary pattern designed inside a microprocessor to perform a specific function. The entire group of instructions that a microprocessor