GATE Overflow Test Series | Computer Organization and Architecture | Test 1 | Question: 14

Question

Consider a CPU where all the instructions require $8$ clock cycles to complete execution. There are $150$ instructions in the instruction set. It is found that $132$ control signals are needed to be generated by the control unit. While designing the horizontal microprogrammed 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 (in bits)?

• A. $134, 10$
• B. $143, 10$
• C. $143, 11$
• D. $134, 11$

Answer 1

Each $150$ instructions require $8$ clock cycles.

This means total number of microinstructions $=150\times 8 = 1200$

We will need $\left\lceil \log_2 1200  \right\rceil = 11$ bits to address them.

Horizontal microprogramming means we will use a separate bit for each of the control signals.

So, size of control word = $132 + 11 = 143$ and control address register size $= 11$ bits.

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One micro instruction takes one clock cycle ? If yes then how it’s always true?