A control unit whose binary control values are saved as words in memory is called a microprogrammed control unit.
A controller results in the instructions to be implemented by constructing a definite collection of signals at each system clock beat. Each of these output signals generates one micro-operation including register transfer. Thus, the sets of control signals are generated definite micro-operations that can be saved in the memory.
Each bit that forms the microinstruction is linked to one control signal. When the bit is set, the control signal is active. When it is cleared the control signal turns inactive. These microinstructions in a sequence can be saved in the internal ’control’ memory. The control unit of a microprogram-controlled computer is a computer inside a computer.
The following image shows the block diagram of a Microprogrammed Control organization.
There are the following steps followed by the microprogrammed control are −
The address that is supported to the control ROM originates from the micro counter register. The micro counter received its inputs from a multiplexer that chooses the output of an address ROM, a current address incrementer, and an address that is saved in the next address field of the current microinstruction.
There are the following advantages of microprogrammed control are as follows −
There are the following disadvantages of microprogrammed control are as follows −