Wang LOCI-2 Circuit Board 1501A

This board is involved with decoding of instructions from the keyboard and punched card programmer.

The board contains an instruction register made from six flip flops located on the right edge of the board. The instruction register is loaded with an instruction code when a key on the keyboard is pressed, or, when the calculator is running a program, the instruction register is loaded from the current step on the punched card pointed to by the PC (Program Counter) register. The content of the instruction register is decoded into 45 different control signals by a large array of diode logic gates that consume the vast majority of the real-estate on the board. These control signals are routed to the other boards to implement the particular function commanded by the instruction.