The microinstructions stored in the control memory of a processor have a width…
2004
The microinstructions stored in the control memory of a processor have a width of 26 bits. Each microinstruction is divided into three fields: a micro-operation field of 13 bits, a next address field (X), and a MUX select field (Y). There are 8 status bits in the inputs of the MUX.
How many bits are there in the X and Y fields, and what is the size of the control memory in number of words?
Answer: A. 10, 3, 1024 — Key facts: microinstruction width = 26 bits; micro-operation field = 13 bits; remaining bits = X + Y = 13. Determine Y (MUX select field): the MUX has 8…
- A.
10, 3, 1024
- B.
8, 5, 256
- C.
5, 8, 2048
- D.
10, 3, 512
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Correct answer: A
Key facts: microinstruction width = 26 bits; micro-operation field = 13 bits; remaining bits = X + Y = 13.
Determine Y (MUX select field): the MUX has 8 status-bit inputs, so the select field must be log2(8) = 3 bits. Therefore Y = 3.
Determine X (next-address field): X = 26 - 13 - Y = 26 - 13 - 3 = 10 bits.
Control memory size (number of words): 2^X = 2^10 = 1024 words.
Answer: X = 10 bits, Y = 3 bits, control memory size = 1024 words.
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