Instruction Sets in 8086 Microprocessor

Definition of Instruction and Instruction Sets in 8086 Microprocessor

Instruction is a command or a binary pattern given to a computer to perform a specific operation on given data/Operand.  Instruction is actually a command to the microprocessor to perform a given task on specified data.

The entire group of these instructions is called Instruction Sets which determines what functions the microprocessor should perform.

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Based on the nature of the operation of instruction, 8086 Instruction Sets can be classified as follow:

Table of Content:

1. Data Transfer Instructions
• General Purpose Byte or Word Transfer Instructions
• Simple Input and Output port Transfer Instructions
• Special Address Transfer Instructions
2. Arithmetic Instructions
• Addition Instructions
• Subtraction Instructions
• Multiplication Instructions
• Division Instructions
3. Bit Manipulation Instructions
• Logical Instructions
• Shift Instructions
• Rotate Instructions
4. Program Execution Transfer Instructions
• Unconditional Transfer Instructions
• Conditional Transfer Instructions
5. Processor Control Instructions
6. String Instructions

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Instructions Sets in 8085 Microprocessor

1. Data Transfer Instructions

1.1 General Purpose Byte or Word Transfer Instructions

Instructions	Comments
MOV Destination, Source Eg: MOV CX,04H	- Copy byte or word from specified Source to Destination
PUSH Source Eg: PUSH BX	- Copy specified word to top of the stack
POP Destination Eg: POP AX	- Copy word from top to stack to specified location.
XCHG Destination, Source Eg: XCHG AX, BX	- Exchange word or byte.

1.2 Simple Input and Output port Transfer Instructions

Instructions	Comments
IN AX,Port_Address Eg: IN AX,34H	- Copy a byte or word from a specified port to accumulator.
OUT Port_Address, AX Eg: OUT 2CH, AX	- Copy a byte or word from accumulator to specified port

1.3 Special Address Transfer Instructions

Instructions	Comments
LEA Register, Source Eg: LEA BX, PRICE	- Load effective address of operand into a specified register
LDS Register, Source Eg: LDS BX,[4326H]	- Load DS register and other specified registers from memory.

2. Arithmetic Instructions

2.1 Addition Instructions

Instructions	Comments
ADD Destination, Source Eg: ADD AL,74H	- Add specified byte to byte or word to word
ADC Destination, Source Eg: ADC CL, BL	Add byte+byte + carry flag Add word+word + carry flag
INC Register Eg: INC CX	- Increment specified byte or word by 1.
AAA	- ASCII adjust after addition.
DAA	- Decimal adjusts after addition.

2.2 Subtraction Instructions

Instructions	Comments
SUB Destination, Source Eg: SUB CX, BX	- Subtract byte from byte or word from word.
SBB Destination, Source Eg: SBB CH, AL	Subtract byte and carry flag from byte Subtract word and carry flag from word
DEC Register Eg: DEC CX	- Decrement specified byte or word by 1.
NEG Register Eg: NEG AL	- form 2's Complements
CMP Destination, Source Eg: CMP CX, BX CF ZF SF CX = BX 0 1 0 CX > BX 0 0 0 CX < BX 1 0 1	- Compare two specified bytes or words.
AAS	- ASCII adjust after subtraction.
DAS	- Decimal adjusts after subtraction.

2.3 Multiplication Instructions

Instructions	Comments
MUL Source Eg: MUL CX	- Multiply unsigned byte by byte or unsigned word by word. - When a byte is multiplied by the content of AL, the result is kept into AX. - When a word is multiplied by the content of AX, MS Byte in DX and LS Byte in AX.
IMUL Source Eg: IMUL CX	- Multiply signed byte by byte or signed word by word
AAM	- ASCII adjust after multiplication. It converts packed BCD to unpacked BCD.

2.4 Division Instructions

Instructions	Comments
DIV Source Eg: DIV BL DIV CX	- Divide unsigned word by byte or, - Divide unsigned word double word by byte. - When a word is divided by byte, the word must be in AX register and the divisor can be in a register or a memory location. - After division AL (quotient) AH (remainder) - When a double word is divided by word, the double word must be in DX: AX pair and the divisor can be in a register or a memory location. - After division AX (quotient) DX (remainder)
AAD	- ASCII adjust before the division - BCD to binary convert before division.
CBW	- Fill upper byte of a word with copies of a sign bit of lower byte.
CWD	- Fill upper word of a double word with a sign bit of lower word.

3. Bit Manipulation Instructions

3.1 Logical Instructions

Instructions	Comments
NOT Destination Eg: NOT BX	- Invert each bit of a byte or word.
AND Destination, Source Eg: AND BH, CL	- AND each bit in a byte/word with the corresponding bit in another byte or word.
OR Destination, Source Eg: OR AH, CL	- OR each bit in a byte or word with the corresponding bit in another byte or word.
XOR Destination, Source Eg: XOR CL, BH	- XOR each bit in a byte or word with the corresponding bit in another byte or word.

3.2 Shift Instructions

Instructions	Comments
SHL Destination, Count CF <- 0="" lsb="" msb="" td="">	- Shift Bits of Word or Byte Left, Put Zero(s) in LSB.
SHR Destination,Count 0 -> MSB LSB -> CF	- Shift Bits of Word or Byte Right, Put Zero(s) in MSB.
SAR Destination, Count MSB->MSB LSB->CF	- Shift Bits of Word or Byte Right, Copy Old MSB into New MSB

3.3 Rotate Instructions

Instructions	Comments
ROL	- Rotate Bits of Byte or Word Left, MSB to LS and to CF.
ROR	- Rotate Bits of Byte or Word Right, LSB to MSB and to CF.
RCL	- Rotate Bits of Byte or Word Left, MSB to CF and CF to LSB.
RCR	- Rotate Bits of Byte or Word Right, LSB TO CF and CF TO MSB.

4. Program Execution Transfer Instructions

4.1 Unconditional Transfer Instructions

Instructions	Comments
CALL	- Call a Subprogram/Procedure
RET	- Return From Procedure to Calling Program.
JMP	- Goto Specified Address to Get Next Instruction (Unconditional Jump to Specified Destination).

4.2 Conditional Transfer Instructions

Instructions	Comments
JC	- Jump if Carry Flag CF=1.
JNC	- Jump if No Carry i.e. CF=0
JE/JZ	- Jump if Equal/Jump if Zero Flag (ZF=1).
JNE/JNZ	- Jump if Not Equal/Jump if Not Zero(ZF=0)
JNO	- Jump if No Overflow.
JO	- Jump on Overflow
JP/JNP	- Jump if Parity/Jump if Not Parity
JPO/JPE	- Jump if Parity Odd. / Jump if Parity Even (PF=1
JS/JNS	- Jump on Sign(SF=1)/Jump if Not Sign(SF=0)
LOOP	- Loop Through a Sequence of Instructions Until CX=0(count register).
JCXZ	- Jump to Specified Address if CX=0.

5. Processor Control Instructions

Instructions	Comments
STC	- Set Carry Flag CF to 1.
CLC	- Clear Carry Flag to 0.
CMC	- Complement the State of CF
STD	- Set Direction Flag to 1.
CLD	- Clear Direction Flag to 0
STI	- Set Interrupt Flag to 1. (Enable INTR Input)
CLI	- Clear Interrupt Enable to 0
NOP	- No Action Except Fetch and Decode
HLT	Halt (Do Nothing) Until Interrupt or Reset.

6. String Instructions

Instructions	Comments
MOV S/ SB/ SW	- Move Byte or Word From One String to Another.
STO S/ SB/ SW	- Store String Instruction
LOD S/ SB/ SW	- Load String Instruction
CMP S/ SB/ SW	- Compare Two String Bytes or Two String Words
SCA S/ SB/ SW	- Compares a Byte in AL or Word in AX With a Byte or Word Pointed By DI in ES.
REP	- Repeat Instruction Until CX=0.
REP E/REP Z	- Repeat if Equal/Repeat if Zero
REP NE/ REP NZ	- Repeat if Not Equal/Repeat if Not Zero.

Conclusion: 
So these are the Instruction sets in 8086 Microprocessor which helps in performing different operations.


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• 8085 Microprocessor Features, Pin Diagram, Architecture
• 8086 Microprocessor Features, Architecture
• All 8085 Instructions with Operand, Size, Addressing Mode, Machine Cycle, T-States
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