About the project

Goal of the project is the development and the realization of a 16 bit relay CPU. To save money and to safe space diodes are also used. The system was simulated using the game "Logic World".

Why? Just for fun...like a railway model or a RC controlled plane. And "High performace" relay computer? Well, its a 16 bit machine, thats not bad for a relay computer.


The system ist a very simple CPU using an Accu register like CPUs in the 80s. The following table shows the command set of the CPU, the picture below the register structure.

Command set

The CPU is able to adress the memory using 3 different adressing modes. a) LD X is loading the Accu with the dataword stored in the adress after the opcode, b) LD M(X) is loading the Accu with the data stored in the memory adress stored after the opcode, and c) LD M(M(X)) is ... yes, indirect adressing. The dataword after the opcode contains the adress where the CPU finds the adress of the dataword that will be stored in the Accu. Is adressing mode c) really necessary? Maybe not. But it makes it easier.

And, as you can see, a CALL / RET set of operations is also avaliable. No, there is no stack realized, only one subroutine level is possible. The return adress is stored in the register SR.

CPU structure

The CPU is a classical Accu machine. All mathematical operations are using the Accu, also all store / load operations. And, because it is a "High Performance" relay system, the program counter has its own adder which is only able to add 1 to the program counter.

Status of the project

The simulation is running very well, all commands of the command set are tested. A more complex programm, a multiplication using shift operations, will be the last test of the simulation.

The circuit diagram is finished, you can find it in the design part.

And the realization startet with the instruction register...and this first module will be finished (thats the plan) until end of march 2023. How long will it take to build the complete system? At least 1 year, but may be 2 years.

If you want to contact me...