Trishna book for gate

Question

In a micro programmed control unit, a control field of one address control instruction has to support two groups of control signals. In group 1 it is required to generate either one or none of the 32 control signals. In group 2 at most 5 from the remaining, what will be the number of bits needed for the control field?

A 8.  B 10.   C  35.   D 37.

Comments

one or none :- So at a time we need only one control signal to be generated so it is vertical microprogrammed. We can use a decoder which is capable of giving 32 out. so no. of input lines in decoder we be log(32)=5

atmost 5 :-  so at a time maximum of 5 signal need to be generated so we can use, horizontal microprogrammed. 

total no. of bits for control field =5+5 => asking about field in control word

http://fourier.eng.hmc.edu/e85_old/lectures/processor/node11.html

Answer 1

In Group 1: We can use vertical micro programming since it needs either of 32 signals at a time,so only only one signal is needed to connect to the required gate or register at a time,we can use a 5 to 32 decoder to represent any of the 32 signals,so 5 bits can choose 32 distinct signals.
In Group 2:We need at most 5,i.e we may need none or 1 or 2..or 5 signals at a time so in worst case we need to give signals to five devices.so here 5 bits is required.
Total 5+5=10 bits.
Answer is B)10

Comments

@SJ how to select none of 32 signals? As given in the question.

Answer 2

one or none :- So at a time we need only one control signal to be generated so it is vertical microprogrammed. We can use a decoder which is capable of giving 32 out. so no. of input lines in decoder we be log(32)=5

atmost 5 :-  so at a time maximum of 5 signal need to be generated so we can use, horizontal microprogrammed. 

total no. of bits for control field =5+5 => asking about field in control word



http://fourier.eng.hmc.edu/e85_old/lectures/processor/node11.html