8085 Classification of Instructions

Classification of Instruction Set of 8085:

8085 Instructions can be classified based on the addressing mode used, size they occupy in memory or by the functions they perform. Figure-1 shows the classification of the instructions

Figure-1:  Classification of Instruction Set of 8085:

Instructions Based on Size :

These instructions can be classified are as follows:

  1. One byte Instructions: These instructions are of one byte in size and hence occupy one memory location in RAM. Examples are CMA, RLC, RRC, RAL, RAR, STC, CMC etc. These instructions do not require any operand to be specified with the instructions, instead the operand is implied in the instructions.
  2. Two Byte Instruction: These instructions of two byte(16-bits) in size and hence will occupy two memory locations in RAM. Examples of such instructions are MVI C,0A;
  3. Three Byte Instructions: These are of three byte in size and hence occupy three locations in memory(RAM). Examples of such instructions are CALL, JMP etc.

Instructions Based on the functions: Based on the functions Instructions can be classified as :

Classification based on Addressing Mode:

Instructions Supporting Immediate mode addressing:

ADI, SUI, ACI, SBI,  ANI, XRI, ORI, CPI, LXI

Instructions Supporting Implied Mode addressing

CMA (Complement the Accumulator)

RAL (Rotate Accumulator left through carry)

RAR (Rotate accumulator right through carry)

XCHG (Exchange the content of H-L register pair with D-E register pair)

RLC (Rotate Left)

RRC (Rotate Right)

CMC (Complement Carry)

STC  (Set Carry)

RIM (Read Interrupt Mask)

SIM (Set Interrupt mask)

Instructions Supporting Direct Register Mode

MOV Rd, Rs

Instructions Supporting Direct Addressing mode

LHLD Addr

LDA Addr

STA Addr

SHLD Addr

Instructions Supporting Indirect Addressing Mode

LDAX [Rp]    ; Will load accumulator with data from address given in register pair Rp(BC, DE, HL)

STAX [Rp]     ; Will store data given in accumulator in memory at address given in register pair Rp.

MOV A, M

MOV M, A

Updated: September 1, 2020 — 4:16 pm

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