Number of instructions in 8085 Microprocessor


INTEL 8085 has a very enriched Instruction Set. Varieties of instructions it can execute. Instructions will have different Byte counts, ranging from 1-Byte to 3-Bytes. Opcode always occupies 1-Byte in the memory. As we know that, with 8 bits for the opcode, 28 = 256 distinct opcodes are possible. In hexadecimal notation, the opcodes can range from 00H to FFH. Each opcode will correspond to an instruction. Thus from the calculation, it is possible to have 256 instructions in the instruction set of 8085. However, only 246 opcodes are implemented in 8085. They can be classified under 66 types, which are broadly classified into the six groups as depicted below −

DescriptionNo. of opcodesNo. of instruction typesExample
Data transfer Instructions8313MOV, MVI etc.
Arithmetic Instructions6214ADD, SUB etc.
Logical Instructions4315AND, XOR etc.
Stack Instructions159PUSH, POP etc.
Branch Instructions368JMP, JZ etc.
I/O Instructions22IN, OUT etc.
Interrupt Instructions55RST 0, RST 1 etc.

Out of these 246 opcodes, we have −

202 Opcodes which are 1-Byte longMOV A, B
18 Opcodes which are 2-Bytes longMVI A, d8
ANI d8
26 Opcodes which are 3-Bytes longJMP d16
LXI B, d16
Published on 27-Dec-2018 12:48:06