The following is a TOY-8 CPU, a simplified version of the TOY CPU.
Toy-8 CPU WS is an extended version with shifters.
The above circuit is build using Logism-Evolution.
https://github.com/logisim-evolution/logisim-evolution
• Open the circuit in Logism-Evolution.
• Go to the Interface circuit to view the user controls.
• To begin inputting your program, first enable Auto-Tick from the Simulate Tab.
• Ideally set the Auto-Tick Frequency to 2Hz, but faster work as well.
• Then load your program by inputting the address and the data.
• Hold the LOAD button for a second to load that value.
• Once done, disable Auto-Tick and if the clock is high, click it one to set it to low.
• Also set the data and address input to 0.
• Then click on the RUN button to enable the CPU. This will be evident by the LED turning green.
• Then just enable Auto-Tick again and watch it run.
• It will come to halt at the end of the program.
| Opcode | Operation | Pseudocode |
|---|---|---|
| 0 | Halt | Halt |
| 2 | Add | R = R + M[addr] |
| 3 | Left Shift | R = R * 2 |
| 4 | Bitwise AND | R = R & M[addr] |
| 5 | Right Shift | R = R / 2 |
| 6 | Bitwise XOR | R = R ^ M[addr] |
| 8 | Load Addr | R = addr |
| A | Load | R = M[addr] |
| C | Store | M[addr] = R |
| E | Branch | if (R == 0) PC = addr |
*Note: For left/right shift, the value in the address part can be anything. It does not effect the operation.