hypxr-7 / toy-8_cpu

A simplied version of the TOY CPU built using logism

TOY-8 CPU in Logism

The following is a TOY-8 CPU, a simplified version of the TOY CPU.
Toy-8 CPU WS is an extended version with shifters.

PREREQUISITES

The above circuit is build using Logism-Evolution.
https://github.com/logisim-evolution/logisim-evolution

How To Use

• 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.

INSTRUCTION SET

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.