The FROG is a tiny 4-bit processor intended to be incorporated into the TinyTapeout multi-project chip on a multi-project wafer
The FROG is an extremely minimal load-store 4-bit CPU. Specified, designed, and tested in less than a day (given I discovered TinyTapeout with 36 hours remaining), several structures were simplified for speed of design.
Registers: 4-bit, A and B ALU Width: 4-bit Address Width: 6-bit Instructions: 15+NOP
| OPCode | Hex | Description |
|---|---|---|
| NGA | 0 | 2's complement negation of A |
| AND | 1 | A = A AND B |
| OR | 2 | A = A OR B |
| XOR | 3 | A = A XOR B |
| SLL | 4 | A = A << B |
| SRL | 5 | A = A >> B |
| SRA | 6 | A = A >> B (preserve sign) |
| ADD | 7 | A = A + B |
| NOP | 8 | No Operation |
| BEQ ofst | 9 AddrH AddrL | If A == B, PC = PC + offset |
| BLE ofst | A AddrH AddrL | If A <= B, PC = PC + offset |
| JMP addr | B AddrH AddrL | PC = addr |
| LDA addr | C AddrH AddrL | A = [addr] |
| LDB addr | D AddrH AddrL | B = [addr] |
| STA addr | E AddrH AddrL | [addr] = A |
| STB addr | F AddrH AddrL | [addr] = B |
The Makefile has been modified to support the same github action as the template repository without actually pulling from Wokwi.