GATE CS 2020 Set 1 — Question 54
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Computer Organization & Architecture → Instructions & Addressing Modes → Instruction Formats
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Question
A processor has 64 registers and uses 16-bit instruction format. It has two types of instructions: I-type and R-type. Each I-type instruction contains an opcode, a register name, and a 4-bit immediate value. Each R-type instruction contains an opcode and two register names. If there are 8 distinct I-type opcodes, then the maximum number of distinct R-type opcodes is _______.
Correct answer
14 to 14
Solution
1.Instruction Format Parameters:
- Total instruction length = 16 bits.
- Number of registers = 64 Register field length = bits.
- Format: Opcode + Register + Immediate
- Fields: Opcode ( bits) + 6 bits (Reg) + 4 bits (Imm)
- Total length: bits.
- Total encoding space for I-type = (Number of I-opcodes) (Register combinations) (Immediate combinations)
- Space used = .
- Format: Opcode + Register + Register
- Fields: Opcode ( bits) + 6 bits (Reg) + 6 bits (Reg) = 12 bits for operands.
- Let be the number of R-type opcodes.
- Space used by R-type = .
- Total space available with 16 bits = .
- The sum of space used by I-type and R-type must be .
- Divide by :
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