Determine the width of Micro-instruction having following Control signal field, in a vertical Micro-programmed Control Unita) Next Address field of 5 Bitsb) ALU Function field selecting 1 out of 7 ALU Functionc) Register-in field selecting 1 out of 15 Registersd) Register-out field selecting 1 out of 15 Registers.e) Shifter field selecting no shift, right shift or left shiftf) Auxiliary control field of 3 bitsa)22b)21c)24d)25Correct answer is option 'B'. Can you explain this answer?

Question

Answer

To determine the width of a micro-instruction in a vertical micro-programmed control unit, we need to consider the number of bits required for each control signal field.

Next Address Field:
The next address field requires 5 bits. This means that we can have up to 2^5 = 32 different next addresses.

ALU Function Field:
The ALU function field selects 1 out of 7 ALU functions. To represent 7 different functions, we need 3 bits because 2^3 = 8, which is greater than 7.

Register-in Field:
The register-in field selects 1 out of 15 registers. To represent 15 different registers, we need 4 bits because 2^4 = 16, which is greater than 15.

Register-out Field:
The register-out field also selects 1 out of 15 registers. Therefore, we need 4 bits to represent 15 different registers.

Shifter Field:
The shifter field selects no shift, right shift, or left shift. To represent these 3 options, we need 2 bits because 2^2 = 4, which is greater than 3.

Auxiliary Control Field:
The auxiliary control field requires 3 bits.

Total Width of the Micro-instruction:
To determine the total width of the micro-instruction, we sum up the number of bits required for each control signal field:

5 bits (Next Address Field) + 3 bits (ALU Function Field) + 4 bits (Register-in Field) + 4 bits (Register-out Field) + 2 bits (Shifter Field) + 3 bits (Auxiliary Control Field) = 21 bits

Therefore, the width of the micro-instruction is 21 bits.

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