Lecture 18: Difference between Microprogrammed and Hardwired Control Unit

#MicroprogrammedControlUnit #ControlUnitTypes
Microprogrammed Control Unit:
The function of the control unit in a digital computer is to initiate sequences of microoperations. The number of different types of microoperations that are available in a given system is finite. The complexity of the digital system is derived from the number of sequences of microoperations that are performed. When the control signals are generated by hardware using conventional logic design techniques, the control unit is said to be hardwired. Microprogramming is a second alternative for designing the control unit of a digital computer.
A computer that employs a micro programmed control unit will have two separate memories: a main memory and a control memory. The main memory is available to the user for storing the program. The contents of main memory may alter when the data are manipulated and every time that the program is changed. The user’s program in main memory consists of
machine instructions and data. In contrast, the control memory holds a fixed microprogram that cannot be altered by the occasional user. The microprogram consists of microinstructions that specify various internal control signals for execution of register microoperations. Each machine
instruction initials a series of microinstructions in control memory. These microinstructions generate the microoperations to fetch the instruction from main memory; to evaluate the effective address, to execute the operation specified by the instruction, and to return control to the fetch phase in order to repeat the cycle for the next instruction.

MICROPROGRAMMED VS HARDWIRED CONTROL UNIT