Hello I am trying to connect 27256 eprom with 74ls163 counter. As my understanding 27256 has A0-A14 address and D0-D7 data bus. Actually I want to see how PC work with ROM memory. I am trying to explain if somewhere wrong. Please correct me. ROM is permanent memory, once it programmed. It doesn't change its data. Here is small example where data and instructions stored in program memory. Code (Text): Address data Address 1 01110000 Address 2 01101110 Address 3 10010001 Now program counter read first 0111000 and store into instruction register. Than read second second and stored into instruction register same for third, read 10010001 and stored into instructions register. No instructions Please look at diagram. If all is correct than I will try to add instructions register.