Difference between Hardwired Control Unit and Microprogrammed Control Unit

Hardwired Control Unit

A hardwired control is a structure of making control signals using Finite State Machines (FSM) suitably. It is created as a sequential logic circuit. The final circuit is generated by physically linking the components including gates, flip flops, and drums are known as the hardwired controller.

Microprogrammed Control Unit

A control unit whose binary control values are saved as words in memory is called a microprogrammed control unit.

In these instructions, the control memory is considered to be ROM, where all the information is saved permanently. The memory address of the control unit denotes the address of microinstruction.

The microinstruction has a control word. The control word indicates the operations for the data processor. After the integration of these operations, the next address should be definite by the control. The next address can be the one that is next in sequence or the one that is situated anywhere.

It is needed that various bits of the current microinstruction is used in the next instruction. There is another method for the next address generator is the microprogram sequencer. The current address is influenced by the control data register until the next address is evaluated and read from the memory. The data register is also called the pipeline register.

Let us see the comparison between Hardwired Control Unit and Microprogrammed Unit.

Hardwired Control UnitMicroprogrammed Unit
It is not applicable to change the structure and instruction set, once it is developed.It is applicable to make modifications by changing the microprogram saved in the control memory.
The design of the computer is complex.The design of the computer is simplified.
The architecture and instructions set are not specified.The architecture and instruction set is specified.
It is quick.It is moderate comparatively.
It has a processor to create signals to be executed in the right sequence.It facilitates the microsequencer from which instruction bits are decoded and executed.
It operates through the need for drums, flip flops, flip chips, and sequential circuits.It controls the sub-devices including ALU, registers, buses, instruction registers.

Updated on: 24-Jul-2021

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