MIPS R-Type Instruction

Abstract

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+--------+------+------+------+------+------+
| Opcode |  Rs  |  Rt  |  Rd  | Shamt| Funct|
| 6 bits |5 bits|5 bits|5 bits|5 bits|6 bits|
+--------+------+------+------+------+------+

• Opcode is always 000000
• funct combined with opcode exactly specifies the instruction
• rs specifies register containing first operand
• rt specifies register containing second operand. Set to 0 for shift instructions
• rd specifies register which will receive result of computation
• shamt for sll and srl. Set to 0 for non-shift instructions

2 types of instructions

1. arith $rd, $rs, $rt
2. shift $rd, $rt, shamt

Important

R format instructions has only registers as Instruction Operand except the shift instructions.

Function Code

• 6 bits
• Give MIPS (2^6-1) + 2^6 = 127 instead of 2^6=64 Instruction
• Dedicated for MIPS R-Type Instruction

Examples

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srl

• Shift Right Logical
• Source Register is 0
• Shifts the value right by n bits, discarding the lower n bits
• Dividing the value in register $s0 by 16 (2^4) - srl $s0, $s0, 4

Terminologies

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Destination Register

• 5bits
• Labeled rd, mapped to WR
• Register that gets the result of Operation in MIPS R-Type Instruction Instruction