Recall that the MC14500B does not have a program counter so it has to be implemented external to the chip. So the program store is straightforward, an 8-bit counter coupled to an 8-bit wide ROM.

The counter in Logisim has many features but we use only some of them.

The high nybble of the code byte is the operation and the low nybble is the address of the port or scratchpad memory.