A microprogrammed control unit is required to generate a total of 25 control…
1996
A microprogrammed control unit is required to generate a total of 25 control signals. Assume that during any microinstruction, at most two control signals are active. The 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
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Correct answer: C
Since at most two control signals can be active in any microinstruction, the control word can use two encoded fields. Each field selects one control signal out of 25. The number of bits needed for one such field is ceil(log₂25) = 5, because 2⁴ = 16 is insufficient and 2⁵ = 32 is sufficient. Therefore, for two simultaneously active control signals, the minimum number of bits is 2 × 5 = 10.