Prerequisite – Hardwired and Micro-programmed Control Unit
Control unit generates control signal using one of the two organizations: Hardwired Control Unit, Microprogrammed Control Unit.
Hardwired Control Unit:
It is implemented as logical circuit (gates, filp-flops, decoders etc.) in the hardware. This organization is very complicated if we have a large control unit.
In this organization, if the design has to be modified or changed, requires changes in the wiring among the various components. Thus the modification of all the combinational circuits may be very difficult.
Microprogrammed Control Unit:
A microprogrammed control unit is implemented using programming approach. A sequence of micro-operations are carried out by executing a program consistingof micro-instructions.
Micro-program, consisting of micro-instructions is stored in the control memory of the control unit. Execution of a micro-instruction is responsible for generation of a set of control signals.
Difference between Hardwired and Microprogrammed Control Unit:
|ATTRIBUTES||HARDWIRED CONTROL UNIT||MICROPROGRAMMED CONTROL UNIT|
|1. Speed||Speed is fast||Speed is slow|
|2. Cost of Imlementation||More costlier.||Cheaper.|
|3. Flexibility||Not flexible to accommodate new system specification or new instruction redesign is required.||More flexible to accommodate new system specification or new instruction sets.|
|4. Ability to Handle Complex Instructions||Difficult to handle complex intruction sets.||Easier to handle complex intruction sets.|
|5. Decoding||Complex decoding and sequencing logic.||Easier decoding and sequencing logic.|
|6. Applications||RISC Microprocessor||CISC Microprocessor|
|7. Instruction set of Size||Small||Large|
|8. Control Memory||Absent||Present|
|9. Chip Area Required||Less||More|
|10. Occurrence||Occurrence of error is more||Occurrence of error is less|
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