The CPU uses various 8-bit and 16-bit wide Registers to store temporarily data. The 8-bit wide Registers are directly connected to the 8-bit wide Data Bus, where the 16-bit wide Registers are connected to the 16-bit wide Address Bus. Each Register is based on the 74LS173 TTL chip, which implements a simple Flip-Flop. Multiple 74LS173 TTL chips are chained up to create 8-bit and 16-bit wide Registers.

Each register PCB board has the following pins:

  • Power (VCC, GND)
  • Clock Signal
  • Input Connection
  • Output Connection
  • Write Control Line
  • Read Control Line

Data on the Input Connection is written into the Register when the Write Control Line and the Clock Signal goes high. Data is returned back at the Output Connection when the Read Control Line and the Clock Signal goes high. The Read and Write Control Line Signals are generated by the Instruction Decoder based on the current executing instruction. The various Registers are connected through a 74LS126 TTL chip (Tri-State Buffer) to the Data Bus and Address Bus.

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