README
This repository contains multiple small CPUs, simulated in Logisim. I abandoned this in favor of this.
Models
cpu8_v1
Extremely simple 8-bit CPU with 6 arithmetic (ADD, SUB) and logical (AND, OR, NAND, NOR) operations, conditional jumps are also supported.
The CPU has 6 Registers:
- 1x Constant loading
- 2x ALU operand
- 1x ALU result
- 2x General purpose
The program is read from a readonly memory (ROM).
Instruction Reference:
The Instruction/Data share 8-bit, the instruction mode is specified by bits 6 and 7, so there is a total of 4 modes:
| Bit | Value | Description |
|---|---|---|
| 6:7 | 00 | Constant loading mode |
| 0:5 | xxxxxx | Number value |
| Bit | Value | Description |
|---|---|---|
| 6:7 | 01 | ALU mode |
| 3:5 | 000 | Reserved |
| 0:2 | 000 001 010 011 100 101 |
And Or Nand Nor Add Sub |
| Bit | Value | Description |
|---|---|---|
| 6:7 | 10 | Copy mode |
| 3:5 | xxx | Source register or input |
| 0:2 | xxx | Target register or output |
| Bit | Value | Description |
|---|---|---|
| 6:7 | 11 | Jump mode |
| 3:5 | 000 | Reserved |
| 0:2 | 000 001 010 011 100 101 110 111 |
Never == 0 < 0 <= 0 Always != 0 > 0 >= 0 |
Programming
In this repository I implemented a simple assembler, to make programming the CPUs easier. The assembler versions (branches) match with the CPU names.