Classification of instructions of

8085 microprocessor

What is instruction?An instruction is a binary pattern designed inside a microprocessor to perform a specific function. The entire group of instructions that a microprocessor supports is called Instruction Set.8085 has 246 instructions. Each instruction is represented by an 8-bit binary value. These 8-bits of binary value is called Op-Code or Instruction Byte.

Classification of instruction2.According to size

3.According to operation

1.According to

addressing modes

1.According to addressing

modes

What is addressing ?Every instruction of a program has to operate on a data.The method of specifying the data to be operated by the instruction is called Addressing.The 8085 has the following 5 different types of addressing modes.

ADDRESSING MODES OF 8085

1.Immediate addressing mode2.Register addressing mode3.Direct addressing mode4.Indirect addressing mode5.Implicit addressing mode

1.Immediate addressing modeIn this mode of addressing ,the data is specified in the instruction itself.The data will be a part of the program instruction.EX. MVI B, 3EH - Move the data 3EH given in the instruction to B register.

2. Register Addressing mode

In register addressing mode, the instruction specifies the name of the register in which the data is available.EX. MOV A, B - Move the content of B register to A register.

3.Direct addressing modeIn direct addressing mode, the address of the data is specified in the instruction.The data will be in memory. In this addressing mode, the program instructions and data can be stored in different memory.EX. LDA 1050H - Load the data available in memory location 1050H in to accumulator in the instruction.

4.Indirect addressing modeIn indirect addressing mode, the instruction specifies the name of the register in which the address of the data is available. Here the data will be in memory and the address will be in the register pair.EX. MOV A, M - The memory data addressed by H L pair is moved to A register.

5.Implicit addressing mode

In implicit addressing mode, the instruction itself specifies the data to be operated.EX. CMA - Complement the content of accumulator; RAL

2.According to size

Instructions in terms of byte size or word size

1.1-byte instruction2.2-byte instruction3.3-byte instruction

1.One byte instructionA one byte instruction includes the

operand and the op-code in same byte.These type of instructions occupy only

one memory location.For example:

Op-code

MOV

ADD

CMA

Operand

C,A

B

--

2.Two byte instructionA two byte instruction includes the op-code

and the 8-bit data or address.This type of instruction occupies 2-memory

location.For example:

Op-code

MVI

IN

Operand

A,O5

01

3.Three byte instructionA 3-byte instruction includes the op-code and

16-bit address or data.This type of instructions occupy three memory

location.For example:

Op-code

LXI

STA

Operand

2050

2051

3.According to operation

TYPES OF INSTRUCTION SET

Data Transfer Instruction Arithmetic Instructions Logical Instructions Branching Instructions Control Instructions

1.Data transfer instructionsThese instructions move data between

registers, or between memory and registers.

These instructions copy data from source to destination.

While copying, the contents of source are not modified.

Op-code• MOV• MOV• MOV• MVI• LDA• STA • LDAX• STAX• LXI• LHLD

Operand • Rd,Rs• R,M• M,R• R,8-bit data• 16-bit address• 16-bit address• Rp• Rp• Rp,16-bit address• 16-bit address

DATA TRANSFER INSTRUCTIONS

Op-code

• SHLD• XCHG• IN• OUT• PCHL• XTHL• SPHL

Operand

• 16-bit address

• 8-bit address• 8-bit address

2.Arithmetic instructions

These instructions perform the operations like:

1. Addition2. Subtract3. Increment4. Decrement

OPERATOR OPRAND DESCRIPTION

ADD R Add data of register with aacumulator

ADD M Add data of register with accumulator

ADC R Add data of register to accumulator with carry

ADC M Add data of memory to accumulator with carry

DAD Reg. pair Add register pair to H-L pair

SUB M Subtract data of memory with accumulator

Arithmetic instruction

OPERATOR OPERAND DESCRIPTION

SBB R Subtract data of register from accumulator

SBB M Subtract data of memory from accumulator

SBI 8 bit data Subtract immediate from accumulator with borrow

INR R Increment in register by +1

DCR R Decrement in register by - 1

INX Rp Increment in register pair by +1

DCX Rp Decrement in register pair by -1

OPERATOR OPERAND DESCRIPTION

ADI 8 bit data Add immediate 8 bit data with accumulator

ACI 8 bit data Add immediate 8bit data to accumulator with carry

SUI 8 bit data Subtract immediate 8 bit data to accumulator with carry

INR M Increment data of memory by +1

DCR M Decrement data of memory by -1

3.Logical instructionsThese instructions perform logical operations

on data stored in registers, memory and status flags.

The logical operations are: AND OR XOR Rotate Compare Complement

Logical instructionsOPERATOR OPERAND DESCRIPTION

ANA R Anding data of register with accumulator

ANA M Anding data of memory with accumulator

ANI 8 bit data Immediate anding of 8 bit data with accumulator

ORA R Oring data of register with accumulator

ORA M Oring data of memory with accumulator

ORI 8 bit data Immediate Oring of 8 bit data with accumulator

XRA R Xoring data of register with accumulator

OPERATOR OPERAND DESCRIPTION

XRA M Xoring data of memory with accumulator

XRI 8 bit data Immediate xoring 8bit data with accumulator

CMP R Compare data of register to accumulator

CMP M Compare data of memory to accumulator

CPI 8 bit data Immediate compare 8 bit data to accumulator

CMA None Complement data of accumulator

CMC None Complement carry flag

OPERATOR OPERAND DESCRIPTION

RLC None Rotate accumulator left without carry

RAL None Rotate accumulator left with carry

RRC None Rotate accumulator right without carry

RAR None Rotate accumulator right with carry

4.Branch control

The branching instruction alter the normal sequential flow.

These instructions alter either unconditionally or conditionally.

Branch control instructions

Op-code

• JMP• Jx• CALL• Cx• RET• Rx• RST

Operand

• 16-bit address• 16-bit address• 16-bit address• 16-bit address• None• None• 0-7

Description

• Jump unconditionally• Jump conditionally• call unconditionally• Call conditionally• Return unconditionally• Call conditionally• Restart (software interrupts)

Op-code

• JC• JNC• JP• JM• JZ• JNZ• JPE• JPO

Description

• Jump if carry• Jump if not carry• Jump if positive• Jump if minus• Jump if zero• Jump if not zero• Jump if even parity• Jump if odd parity

Flag status

• CY=1• CY=0• S=0• S=1• Z=1• Z=0• P=1• P=0

Jump conditionally

Op-code

• CC• CNC• CP• CM• CZ• CNZ• CPE• CPO

Description

• Call if carry• Call if not carry• Call if positive• Call if minus• Call if zero• Call if not zero• Call if even parity• Call if odd parity

Flag status

• CY=1• CY=0• S=0• S=1• Z=1• Z=0• P=1• P=0

Call conditionally

Op-code

• RC• RNC• RP• RM• RZ• RNZ• RPE• RPO

Description

• Return if carry• Return if not carry• Return if positive• Return if minus• Return if zero• Return if not zero• Return if even parity• Return if odd parity

Flag status

• CY=1• CY=0• S=0• S=1• Z=1• Z=0• P=1• P=0

Return conditionally

Instructions

• RST0• RST1• RST2• RST3• RST4• RST5• RST6• RST7

Address

• 0000H• 0008H• 0010H• 0018H• 0020H• 0028H• 0030H• 0038H

Restart address table

5.Stack ,I/O,machine Control Instructions

The control instructions control the operation of microprocessor.

OPERATOR OPERAND DESCRIPTION

LXI SP 16 bit address Load 16-bit address into stack pointer register

PUSH Rp Push data of reg. pair in stack

POP Rp Pop data of reg. pair from stack

PUSH PSW Push data of PSW(accumulator + flag) in stack

POP PSW Pop data of PSW(accumulator + flag) from stack

NOP None No operation perform

HLT None Waiting state

Stack, I/O, Machine control

Op-code

• EI• DI• RIM• SIM

Operand

• NONE• NONE• NONE• NONE

Description

• Enable interrupt• Disable interrupt• Read interrupt mask• Set interrupt mask

Interrupt control instructions