Question

2. [2090] In the MIPS instruction set we discussed in class, explain each field except sa in the three different instruction formats. Give an example instruction for each format. 3 Instruction Formats: all 32 bits wide OP OP Op rs rt rd funct R format I format J format sa rs rt immediate ump target

Answer 1

R - format instruction :

OP - is the opcode or operation code , it is of 6 bits in size

rs - rs is the first source register operand , it is of 5 bits in size

rt - rt is the second source register operand , it is of 5 bits in size

rd - rd is the destination register operand , it is of 5 bits in size

funct - It is the function code, identifies the specific R-format instruction , it is of 6 bits in size

Example : Consider the instruction

     add $s0, $s1, $s2 

the register 16,17,18 are used.

Instruction:

	add $s0, $s1, $s2    # add rd, rs, rt
machine code:	000000 10001 10010 10000 0000 100000 (op rs rt rd shamt funct)

I format instruction :

OP - Operation code of 6 bits in size

rs - register containing base address of 5 bits

rt - register of destination/source of 5 bits

Immediate - value or a offset of 16 bits

Example : Consider an instruction ,

 lw $t0, 32($s3)       (registers 8 and 19)

OP	rs	rt	immediate
35	19	8	32
100011	10011	01000	0000000000100000

J- format instruction :

OP- operation code of 6 bits

jump target address - Address in the instruction 26 bits

Example :

Consider an instruction :

 j LOOP if loop is at address 1028 then 

OP	Address
2	257
000010	00000000000000000100000001