Question

computer has a 32-bit instruction word broken into fields as follows: opcode, six bits; two register file address fields, five bits each; and one immediate operand/register file address field, 16 bits. (a) What is the maximum number of operations that can be specified? (b) How many registers can be addressed? (c) What is the range of unsigned immediate operands that can be provided? (d) What is the range of signed immediate operands that can be provided, assuming that the operands are in 2s complement representation and that bit 15 is the sign bit?

Answer 1

Answer:

a.  2^6, or 64 opcodes.

b.  2^5, or 32 registers.

c. 2^16, or 0 to 65536.

d.  -32768 to 32768.

Explanation:

a. Following that the opcode is 6 bits, it is generally known that the maximum number of opcodes should be 2^6, or 64 opcodes.

b. Now, since the size of the register field is 5 bits, we know that 2^5 registers can be accessed, or 32 registers.

c. Unsigned immediate operand applies to the plus/minus sign of the number. Since unsigned numbers are always positive, the range is from 0 to 2^16, or 0 to 65536.

d. Considering that the signed operands can be negative, they need a 16'th bit for the sign and 15 bits for the number. This means there are 2 * (2^15) numbers, or 2^16. However, the numbers range from -32768 to 32768.