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NQSAP

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

NQSAP Breadboard Computer

Clock bus PC
SP / MAR
Memory A Register
Reset / Loader ALU
Output / IR ALU B Register
Ring Ctr / Addr
uCode ROMs Control LEDs