8-Bit Breadboard Computer

Yes, I built an 8-bit computer on breadboards. It closely follows Ben Eater’s original design.

Go here to see a collection of programs for the computer.

How it Works

Instruction Set

0000 NOP - No OPeration
0001 LDA - LoaD A register with contents of memory address
0010 ADD - ADD contents of given memory address to A
0011 SUB - SUBtract
0100 STA - STore the value in the A register in a given memory address
0101 LDI - LoaD Immediate
0110 JMP - JuMP
0111 JC  - Jump on Carry
1000 JZ  - Jump on Zero
1001
1010
1011
1100
1101
1110 OUT - OUTput the value in the A register
1111 HLT - HaLT

Some possible other instructions to add:

• DSP - DiSPlay the contents of a given memory address
• INC - INCrement A by the given 4 bit value (aka Add Immediate)
• DEC - DECrement A by the given 4 bit value (aka Subtract Immediate)
• JNC - Jump on Not Carry
• JNZ - Jump on Not Zero

Control Signals

• HLT - Halts the program
• MI - Memory address register in
• RI - RAM in
• RO - RAM out
• IO - Instruction Regsiter out
• II - Instruction Register in
• AI - A register in
• AO - A register out
• EO - Sum out (ALU out)
• SU - Subtract
• BI - B register in
• OI - Output in
• CE - Counter enable
• J - Jump
• FI - Flags register in