Microprogramming Control Unit

Question

A hypothetical processor supports 256 instructions.Each instruction takes 12 cycles to complete the execution. Processor supports horizontal control unit design. It has 24 control signals and 16 flags. What is the size of microinstruction??

Answer 1

No of control words=256*12=3072 

12 bits required for address

As horizontal programming is used no of bits for control signal=24

No of bits for flags=4

Control word format is

Signal

flags(condition codes)

next address

So total no of bits in contol word=24+4+12=40

Comments

@AnkitSinghGautam In microprogrammed Instructions, each of the micro-instructions require 1 cycle to execute. So each microprogram requires 12 cycles means that each each microprogram requires 12 micro instructions. So thats why total micro instructions will be 256*12.

 

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Can't  understand why 12bits are required for the address..pls explain

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In microprogrammed control unit instructions are designed in such a way that To execute each micro instruction number of clock cycle needed is always 1.

In question it is given that to execute 1 instruction no of clock cycles needed =12

Therefore we can say that in 12 cycle there are exactly 12  micro operations executed

i.e. number of micro instruction per instruction =12

Total number of micro instruction = number of control word =256*12

 

So number of bits required for address= log2(number of control word) = 12bit