Juno 4-bit homebrew computer

Juno is a 4 bit CPU built from 7400 series logic chips - individual logic gates, counters, registers and the '181 bit-slice ALU. 

It is currently work in progress with the following complete

  • ALU and registers connected to the data and address bus
  • Micro code contoller signal wires in place

Specs

The design specs for the Juno are 

  • 4 bit data bus
  • 8 bit address bus, 256 byte address space
  • Program accessible registers
    • A register
    • PC register
    • Status bits - carry and comparator flags
  • Non program directly accessible registers
    • AR (Address Register)
    • DR (Data Register)
    • IR (Instruction Register)
  • 4 bit '181 ALU - logic and arithmetic operations

 Breadboard

 The Juno is build on breadboards



Architecture 

The architecture for the Juno is shown in the figure below


Design

The following pages describe the design in more detail

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