GATE CSE 1996 | Question: 2.25

Question

A micro program control unit is required to generate a total of $25$ control signals. Assume that during any micro instruction, at most two control signals are active. Minimum number of bits required in the control word to generate the required control signals will be:

• A. $2$
• B. $2.5$
• C. $10$
• D. $12$

Comments

@Vishnathan in case of horizontal programming answer will be 25+25=50 because for every state we need one bit 

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@Vishnathan , Yes there will be 25 bits in the control word in case of Horizontal Programming

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25 control signals given, that requires 5 bits, among that five bit atmost 2 bits are used for activating 2 control signals, hence 5C2 combination can be made. 5c2 = 10

Answer 1

We generate one out of 25 control signals form one 5 * 25 decoder and another one form another  5 * 32 decoder.

 

Answer 2

If we had required them only one at a time . Vertical micro programming would facilitate us ie

ceil(log(25))= 4.64   ==> .   5

if any two were specifically designated to be used simultaneously two at at time we would have taken them seprately in Horizontal microprograming but here any two of the 25 cab be used simutaneousy

so since MINIMUM is asked we would acheive this by doubling our minimum value for one signal ie

5*2 =10