Block Diagram Hardwired Control Unit. Hardwired control unit an instruction read from memory is placed in the instruction register ir. Hard wired control unit is implemented as sequential logic circuit or finite state machine fsm generates controls sg to execute the instruction.
The control memory is programmed to start the needed sequence of micro operations. An instruction fetched from the memory unit is placed in. Two memory units o a main memory for storing.
Furthermore it was very difficult to get the control correct and changing roms was easier than replacing a random logic control unit.
The instruction register is divided into three parts. The outputs of the state machine are the control signals. An instruction fetched from the memory unit is placed in the instruction register ir. Block diagram of control unit is displayed in figure below.