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Consider a CP...

Question

Consider a $C P U$ where all the instructions require $7$ clock cycles to complete execution. There are $140$ instructions in the instruction set. It is found that $125$ control signals are needed to be generated by the control unit. While designing the horizontal micro-programmed control unit, single address field format is used for branch control logic. What is the minimum size of the control word and control address register?

A

125, 10

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B

135, 10

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C

125, 7

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D

135, 9

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Solution

The correct option is A $125, 10$
Control word format:

Number of control address $=$ Number of instruction $\times$ Number of clock cycle
$= 140 \times 7 = 980$

$N u m b e r o f b i t s f o r (C A R) = l o g (980)$
$= 10 b i t s$

Since horizontal $μ$ programming used. So number of bits for control signal
$= 125 b i t s$

So, control word size in bits
$= 125 + 10 = 135$

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