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4bit CPU using relays.
(without ROM & Address decoder)
This circuit is from my relay 4-bit CPU, EMC-110.
The top ramp from left to right represents the A register, B register, input, and output.
The left four of the eight lamps in the center represent opcodes and the right four represent operand.
Originally, these values are displayed as read from ROM, but due to space limitations, they are entered manually.
The lamp slightly above right represents the output of the program counter.
The lower lamps are, from left to right: Zero flag, Carry flag, ALU output, Clock distributor output (A Reg_Clk, B Reg_Clk, Output_Clk, PC_JMP Clk), and for clock indication.
The switch above the clock lamp is for automatic or manual clock switching, and the switch below is for manual clocking.
OpCode Operand Operation
００００ ＸＸＸＸ A ← [Data]
０００１ ＸＸＸＸ B ← [Data]
００１０ A ← B
００１１ B ← A
０１００ A ← A + B
０１０１ A ← A - B
０１１０ ＸＸＸＸ A ← A + [Data]
０１１１ ＸＸＸＸ A ← A - [Data]
１０００ OUT ← A
１００１ OUT ← B
１０１０ ＸＸＸＸ OUT ← [Data]
１０１１ A ← IN
１１００ ＸＸＸＸ PC ← [Address]
１１０１ ＸＸＸＸ PC ← [Address] (C = 1)
１１１０ ＸＸＸＸ PC ← [Address] (Z = 1)
１１１１ HALT (Clock stop)
The instruction set of this CPU is based on that of CPU1738 (https://www.zep.co.jp/nbeppu/article/mz-cpu1738-da1/) and is compatible.
However, the contents of the circuits are almost completely different. In addition to the general instruction decoder, a clock distributor is used as an instruction decoder unique to the relay.
Instead of inputting a clock to all registers each time and selecting update/maintenance by a different signal, the clock signal itself is distributed to control an arbitrary register.
Synchronization is maintained because the circuit itself can be switched. It can be said that this circuit is unique to relays.
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