Introduction to Assembly

Language Programming

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Language Programming

(Instruction Set)

High Level Language

Compiler

Assembly Language

Assembler

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Assembler

Machine Code

Microprocessor Hardware

8085A Instruction Set

• Data Transfer Instruction• Move data between registers or between memory locations

and registers. Includes moves, loads, stores andexchanges.

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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.

Branch/Jump Instruction• Initiates conditional or unconditional jumps, calls,

returns and restart.

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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.

Microprocessor System Block diagram

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Programming Model

0000H

0003H

0001H

0002H

0005H

0004H

A

B

D E

C

FLAG

8 bit

8 bit

00H

03H

01H

02H

05H

04H

8 bit

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0005H

FFFDH

0006H

FFFFH

FFFEH

MEMORY

D E

H L

SP

PC

CPU

05H

FDH

06H

FFH

FEH

I/O

Data Transfer

IMMEDIATE DATA TRANSFER

Move immediate 8 bit

MVI reg , data8 ;data8 � (reg)

Load register pair immediate

LXI rp ,data16 ;data16 � (rp)

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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

Example

MVI A ,10 ;A=0AH

MVI B ,10010001B ;B=91H

MVI D ,7FH ;D=7FH

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LXI B ,3 ;B=00H , C=03H

LXI H ,2345H ;H=23H , L=45H

LXI D ,100 ;D=00H , E=64H

LXI SP,3FF0H ;SPH=3FH,SPL=F0H

Example

MVI B, 55H

MOV A , B

MOV C , A

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MOV C , A

MOV H , CMOV L , A

MOV E , L

HLT

DIRECT DATA TRANSFER

Load Accumulator Direct

LDA address16

Store Accumulator Direct

STA address16

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STA address16

Load H and L Register Direct

LHLD address16

Store H and L Register Direct

SHLD address16

Example

• LDA 3000H

(3000H) � (A)

• STA 2100H

x1

0000H

2100H

0001H

..

2102H

2101H

..

A

x1

STORE

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• STA 2100H

(A)� (2100H)

3000H

..

3509H

y1

..

..A

y1

LOAD

Example

LHLD 8000H

(8000H) � (L)

(8000H + 1) � (H)x1

0000H

3500H

0001H

..

3502H

3501HH

x1

STORE

x2x2

L

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SHLD 3500H

(L) � (3500H)

(H) � (3500H + 1) y2

3502H

8000H

..

3509H

y1

..

8001H

L y1

LOAD

y2H

INDIRECT DATA TRANSFER

Load Accumulator Indirect

LDAX B ;pointer is BC register

LDAX D ;pointer is DE register

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Store Accumulator Indirect

STAX B ;pointer is BC register

STAX D ;pointer is DE register

INDIRECT DATA TRANSFER

Move – copy from memory to register indirect

• MOV reg , M ;pointer is HL register

Move – copy from register to memory indirect

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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

Example

ORG 0000H

LXI B , 2020H

MVI A , 88H

STAX B

INX B

LDAX B

LXI H , 3000H

0000H

0003H

0001H

0002H

0005H

0004H

0006H

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LXI H , 3000H

MOV D , M

MOV M , A88H

AAH

2020H

0006H

3000H

B

D

88H

00H30H

20H 20HA

H L

C2021H

FFH

0000H

0003H

0001H

0002H

0005H

0004H

0006H

• Instruction INX – increment Register pair

• BC = 2021H

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88H

AAH

2020H

0006H

3000H

B

D

AAH

00H30H

FFH

20H 21HA

H L

C2021H

AAH

• Transfer 10 byte data from memory location 3000h

to memory location 3500h using LDA & STA

LDA 3000H

STA 3500H

.

.

x1

x2

0000H

3000H

0001H

..

3001H

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.LDA 3009H

STA 3509H

x2

..

x10

..

..

3001H

3500H

3009H

3509H

x1

x10

..

..

• Transfer 10 byte data from memory location 3000h

to memory location 3500h using LDAX & STAX

MVI H,10

LXI B , 3000H

LXI D , 3500H

LOOP: LDAX B

STAX D

INX B

x1

x2

0000H

3000H

0001H

..

3001H

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INX B

INX D

DCR H

JNZ LOOP

HLT

..

x10

..

..

3500H

3009H

3509H

x1

x10

..

..

Arithmetic Operation

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• ALU

• FLAG

• CPU REGISTER

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

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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)

EXAMPLE

• ADI 99H ; A contains 88 (H)

•register A 1 0 0 0 1 0 0 0 1 3 6 decimal

constant 1 0 0 1 1 0 0 1 1 5 3 decimal

_____________ _____

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register A 1 0 0 1 0 0 0 0 1 2 8 9 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

EXAMPLE

• ADC B ; A contains 88 (H) B contains 99 (H); CY =1

CY 1

register A 1 0 0 0 1 0 0 0

register B 1 0 0 1 1 0 0 1

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register B 1 0 0 1 1 0 0 1_____________

register A 1 0 0 1 0 0 0 1 0

• Flag : S = 0 , Z = 0, AC = 1, P = 1,CY = 1

SUBTRACTIONSubtract immediate from Accumulator

SUI data8 ;(A) - data8 � (A)

Subtract register or memory from Accumulator

SUB reg ;(A) - (reg) � (A)

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Subtract immediate with Borrow SBI data8 ;(A) - data8 - CY � (A)

Subtract source and borrow from Accumulator SBB reg ;(A) - (reg) - CY � (A)

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

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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

Logic Instruction

AND

AND Immediate With Accumulator

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• ANI data8 (A) Λ Data8 � (A)

AND Register/Memory With Accumulator

• ANA reg (A) Λ (Reg) � (A)

OR

OR Immediate With Accumulator

• ORI data8 (A) V Data8 � (A)

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OR Register/Memory With Accumulator

• ORA reg (A) V (Reg) � (A)

EXCLUSIVE-OR

EX-OR Immediate With Accumulator

• XRI data8 (A) ⊕ Data8 � (A)

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EX-OR Register/Memory With Accumulator

• XRA reg (A) ⊕ (Reg) � (A)

Write an assembly language program to clear bit 7 and

set bit 3 and 4 of memory location 3200h.

ORG 2000H

LDA 3200H

ANI 01111111B

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ANI 01111111B

ORI 00011000B

STA 3200H

RST 1

COMPLEMENT THE ACCUMULATOR

• CMA ( ) � (A)A

A

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COMPLEMENT THE CARRY STATUS

• CMC ( ) � (CY)

A

CY

COMPARE

Compare Accumulator With Immediate Data

• CPI data8 (A) – data8

Compare Accumulator With Register/Memory

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Compare Accumulator With Register/Memory

• CMP reg (A) – (reg)

Note: Only flag affected

Write an assembly program to find a largest value between

two number at memory location 3000h and 3001h and store

to memory location 3002h

ORG 2000H

LDA 3000H

MOV B, A

LDA 3001H

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LDA 3001H

CMP B ;(A) – (B)

JNC STORE ;CY=0 IF (A) > (B)

MOV A, B ;CY=1 IF (A) < (B)

STORE: STA 3002H

RST 1

Rotate

Rotate Accumulator Right Through Carry

• RAR (A0) � (CY)

(An+1) � (An)

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(An+1) � (An)

(CY) � (A7)

A0A1A2A3A4A5A6A7CY

Rotate

Rotate Accumulator Left Through Carry

• RAL (A7) � (CY)

(An) � (An+1)

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(An) � (An+1)

(CY) � (A0)

A0A1A2A3A4A5A6A7CY

Rotate

Rotate Accumulator Right

• RRC (A0) � (A7)

(An+1) � (An)

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(An+1) � (An)

(A0) � (CY)

A0A1A2A3A4A5A6A7CY

Rotate

Rotate Accumulator Left

• RLC (A7) � (A0)

(An) � (An+1)

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(An) � (An+1)

(A7) � (CY)

A0A1A2A3A4A5A6A7CY

Branch Instruction

Unconditional Jump

• JMP address16

(Byte 3) (Byte 2) � (PC)

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Conditional Jump

• J Condition address16

If (Condition= true)

(Byte 3) (Byte 2) � (PC)

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

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• 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

Example 1

Check Zero Flag

MVI B, 255

LOOP: DCR B

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LOOP: DCR B

JNZ LOOP ;if Z == 0 then goto

;LOOP

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

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JMP STORE

CHK_EQUAL: JZ EQUAL ;Z == 1?

MVI A,FFH

JMP STORE

EQUAL: MVI A, 80H

STORE: STA 3000H

RST 1

Unconditional Call Subroutine

• CALL address16

(PCH) � ((SP) –1)

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(PCH) � ((SP) –1)

(PCL) � ((SP) –2)

(SP) – 2 � (SP)

(Byte 3)(Byte 2) � (PC)

Conditional Call Subroutine

C Condition address16

If (Condition = True)

(PCH) � ((SP) –1)

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(PCH) � ((SP) –1)

(PCL) � ((SP) –2)

(SP) – 2 � (SP)

(Byte 3)(Byte 2) � (PC)

• 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

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• 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

Return From Subroutine

• RET

((SP)) � (PCL)

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((SP)) � (PCL)

((SP) + 1) � (PCH)

(SP) + 2 � (SP)

Return From Subroutine (Conditional)

• R Condition

If (Condition = True)

((SP)) � (PCL)

((SP) + 1) � (PCH)

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((SP) + 1) � (PCH)

(SP) + 2 � (SP)

• 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

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• 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

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

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LDA 2111H

CALL FIND_SMALL ;call subroutine

STA 2201H

RST 1

FIND_SMALL: CMP B ;Subroutine

JC EXIT

MOV A, B

EXIT: RET

END

I/O,Stack, Machine Control

Instruction

Stack Operation

Write The Content of Register Pair Onto

The Stack

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The Stack

• PUSH rp

(reg high) � ((SP) –1)

(reg low) � ((SP) –2)

(SP) – 2 � (SP)

Write The Content of Accumulator & Flag

Status Onto The Stack

• PUSH PSW

(A) � ((SP) –1)

(Flag) � ((SP) –2)

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(Flag) � ((SP) –2)

(SP) – 2 � (SP)

Retreive The Content of Register Pair

From The Stack

• POP rp

((SP)) � (reg low)

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((SP)) � (reg low)

((SP) + 1) � (reg high)

(SP) + 2 � (SP)

Retreive The Content of Accumulator &

Flag Status From The Stack

• POP PSW

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• POP PSW

((SP)) � (Flag)

((SP) + 1) � (A)

(SP) + 2 � (SP)

STACK OPERATION

Lecture 2

(Revision)

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(Revision)

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

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• 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

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.

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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 rpinstruction.

• Data is automatically transferred from the stack area of memory to the program counter whenever the processor executes a return (ret) instruction.

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.

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• 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

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

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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.

Example

Write a program to exchange the contents

of BC register with DE register

Program 1 Program 2

MOV H,B PUSH B

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MOV L,C PUSH D

MOV B,D POP B

MOV C,E POP D

MOV D,H

MOV E,L

Input/Output Operation

Input From The Port

• IN Port_Address

(port) � (A)

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(port) � (A)

Output To Port

• OUT Port_Address

(A) � (Port)

Example

Input From The Port

IN 80H ;Read from Port 80H

STA 2100H ;Store to Memory

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STA 2100H ;Store to Memory

Output To Port

MVI A, 01H

OUT 81H ;Write 01H to Port 81H

Example: Blink LED at Port A 8255

LXI SP, 3FF0H ;init Stack Pointer

MVI A, 80H

OUT 83H ;Init 8255, all port as output

REPEAT: MVI A,0

OUT 80H

CALL DELAY ;Call subroutine

MVI A,1

OUT 80H

CALL DELAY ;Call subroutine

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CALL DELAY ;Call subroutine

JMP REPEAT

DELAY: MVI B, 0 ;Subroutine

LOOP: DCR B

JNZ LOOP

RET

END

Interrupt

RIM Read interrupt mask

SIM Set Interrupt mask

DI Disable Interrupt

EI Enable Interrupt

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EI Enable Interrupt

(Detail discussion in interrupt topic)

NEXT WEEK

ASSEMBLY LANGUAGE PROGRAMMING

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PROGRAMMING