Instruction set in MPI, Schemes and Mind Maps of Microprocessor and Interfacing

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• INSTRUCTION SET OF

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 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.

Data Transfer Instructions

• These 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.

Data Transfer Instructions

Opcode Operand Description MOV Rd, Rs Rd, M M, Rs Copy from source to destination.  This instruction copies the contents of the source register into the destination register.  The contents of the source register are not altered.  If one of the operands is a memory location, its location is specified by the contents of the HL registers.  Example: MOV B, C  MOV B, M  MOV M, C

Data Transfer Instructions

Opcode Operand Description LXI Reg. pair, 16-bit data Load register pair immediate  This instruction loads 16-bit data in the register pair.  Example: LXI H, 2034 H

Data Transfer Instructions

Opcode Operand Description LDA 16 - bit address Load Accumulator  The contents of a memory location, specified by a 16- bit address in the operand, are copied to the accumulator.  The contents of the source are not altered.  Example: LDA 2034H

Data Transfer Instructions

Opcode Operand Description LHLD 16 - bit address Load H-L registers direct  This instruction copies the contents of memory location pointed out by 16-bit address into register L.  It copies the contents of next memory location into register H.  Example: LHLD 2040 H

Data Transfer Instructions

Opcode Operand Description STA 16 - bit address Store accumulator direct  The contents of accumulator are copied into the memory location specified by the operand.  Example: STA 2500 H

Data Transfer Instructions

Opcode Operand Description SHLD 16 - bit address Store H-L registers direct  The contents of register L are stored into memory location specified by the 16-bit address.  The contents of register H are stored into the next memory location.  Example: SHLD 2550 H

Data Transfer Instructions

Opcode Operand Description XCHG None Exchange H-L with D-E  The contents of register H are exchanged with the contents of register D.  The contents of register L are exchanged with the contents of register E.  Example: XCHG

Addition

• Any 8-bit number, or the contents of register, or the contents of

memory location can be added to the contents of accumulator.

• The result (sum) is stored in the accumulator.
• No two other 8-bit registers can be added directly.
• Example: The contents of register B cannot be added directly to the

contents of register C.

Subtraction

• Any 8-bit number, or the contents of register, or the contents of

memory location can be subtracted from the contents of

accumulator.

• The result is stored in the accumulator.
• Subtraction is performed in 2’s complement form.
• If the result is negative, it is stored in 2’s complement form.
• No two other 8-bit registers can be subtracted directly.

Arithmetic Instructions

Opcode Operand Description ADD R M Add register or memory to accumulator

 The contents of register or memory are added to the contents of

accumulator.

 The result is stored in accumulator.

 If the operand is memory location, its address is specified by H-L pair.

 All flags are modified to reflect the result of the addition.

 Example: ADD B or ADD M

Arithmetic Instructions

Opcode Operand Description ADC R M Add register or memory to accumulator with carry

 The contents of register or memory and Carry Flag (CY) are added to the

contents of accumulator.

 The result is stored in accumulator.

 If the operand is memory location, its address is specified by H-L pair.

 All flags are modified to reflect the result of the addition.

 Example: ADC B or ADC M