The microinstructions stored in the control memory of a processor have a width…
2009
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
- A.
10, 3, 1024
- B.
8, 5, 256
- C.
5, 8, 2048
- D.
10, 3, 512
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Correct answer: A
Total width of microinstruction is 26 bits. Micro-operation field takes 13 bits, leaving 13 bits for the Next Address (X) and MUX Select (Y) fields combined. Since there are 8 status bits for the MUX, the select field Y requires log2(8) = 3 bits. Therefore, the Next Address field X has 13 - 3 = 10 bits. The size of the control memory is determined by the address field X, which gives 2^10 = 1024 words.
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