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move up the instruction encoding part

Kevin Ramharak 2020-07-29 22:18:21 +02:00
parent 782043bee7
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Instruction-Set.md

@ -121,6 +121,25 @@ MOV A, 0x20
This human readable format is parsed by the assembler which will output the actual binary opcodes and operands. This human readable format is parsed by the assembler which will output the actual binary opcodes and operands.
### Instruction encoding
Instructions are 1-3 words long and are fully defined by the first word.
In a basic instruction, the lower 6 bits of the first word of the instruction
are the opcode, and the remaining 10 bits are split into a 5 bit destination operand
and a 5 bit source operand.
In bits, a basic instruction has the format: `sssssdddddoooooo`
Operand value:
| Description | Value |
| --- | --- |
| Invalid or none | `00000` |
| Immediate value at IP+1 | `11111` |
| [Immediate value at IP+1] | `11110` |
| Register | `00001`-`01000` |
| [Register] | `01001`-`10000` |
| Register + Immediate value at IP+1 | `10001`-`11000` |
## Flags ## Flags
Some instructions will change certain flags based on their result. These are in a special non read-write register. These flags are used for the family of jump instructions. You can also use the [`PUSHF`](#pushf) and [`POPF`](#popf) instructions to query and manipulate the flags Some instructions will change certain flags based on their result. These are in a special non read-write register. These flags are used for the family of jump instructions. You can also use the [`PUSHF`](#pushf) and [`POPF`](#popf) instructions to query and manipulate the flags
@ -1052,21 +1071,3 @@ XOR performs a bit-by-bit "exclusive or" on its two operands, and
```py ```py
destination = destination ^ source destination = destination ^ source
``` ```
### Instruction encoding
Instructions are 1-3 words long and are fully defined by the first word.
In a basic instruction, the lower 6 bits of the first word of the instruction
are the opcode, and the remaining 10 bits are split into a 5 bit destination operand
and a 5 bit source operand.
In bits, a basic instruction has the format: `sssssdddddoooooo`
Operand value:
| Description | Value |
| --- | --- |
| Invalid or none | `00000` |
| Immediate value at IP+1 | `11111` |
| [Immediate value at IP+1] | `11110` |
| Register | `00001`-`01000` |
| [Register] | `01001`-`10000` |
| Register + Immediate value at IP+1 | `10001`-`11000` |