The Not Quite Simple As Possible Computer
The NQSAP is a breadboard TTL computer that follows the Ben Eater 8-bit computer (SAP-1) design with some enhancements and extensions.
Highlights of the design are:
- 6502-inspired instruction set that provides equivalents to most of the instructions and addressing modes
- 8-bit addressing extends the size of memory and number of opcodes
- 74LS181 ALU instead of adder provides arithmetic and logic operations including add, subtract, AND, OR, and XOR
- Arduino-based loader/debugger to load programs and run interactive diagnostics
- 3-to-8 Decoders for register selection simplifies wiring and reduces the number of microcode bits needed while also protecting against inadvertent bus collisions
- 8-bit Stack Pointer for storage and subroutines
This repo contains:
- NQSAP documentation
- Arduino-based Microcode programmer
- Arduino Nano-based System Loader / Debugger
| Clock | bus | PC |
| SP / MAR | ||
| Memory | A Register | |
| Reset / Loader | ALU | |
| Output / IR | ALU B Register | |
| Ring Ctr / Addr | ||
| uCode ROMs | Control LEDs |