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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 −
| Description | No. of opcodes | No. of instruction types | Example |
|---|---|---|---|
| Data transfer Instructions | 83 | 13 | MOV, MVI etc. |
| Arithmetic Instructions | 62 | 14 | ADD, SUB etc. |
| Logical Instructions | 43 | 15 | AND, XOR etc. |
| Stack Instructions | 15 | 9 | PUSH, POP etc. |
| Branch Instructions | 36 | 8 | JMP, JZ etc. |
| I/O Instructions | 2 | 2 | IN, OUT etc. |
| Interrupt Instructions | 5 | 5 | RST 0, RST 1 etc. |
| Total | 246 | 66 |
Out of these 246 opcodes, we have −
| Classifications | Examples |
|---|---|
| 202 Opcodes which are 1-Byte long | MOV A, B ANA B |
| 18 Opcodes which are 2-Bytes long | MVI A, d8 ANI d8 |
| 26 Opcodes which are 3-Bytes long | JMP d16 LXI B, d16 |
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