Register Type Instruction Format (R – Type)

This is a group contains all instructions that do not require an immediate value( a value, e.g. 5,-3,etc), target offset, memory address displacement, or memory address to specify an operand. This includes arithmetic and logic with all operands in registers, shift instructions, and register direct jump instructions (jal and jr).

It specify 3 registers(rs,rt,rd), a shift amount field(shamt), and a function field(funct).Opcode for R- type is 000000.

Instruction fields

op	rs	rt	rd	shamt	funct
Operation code	Source register specifier	Target register specifier	Destination register specifier	Shift amount	Function field

         6Bits                         5bits                             5bits                                 5bits                          5bits                   6bits

Instruction coding

-immediate from 0^thbit to 5^thbit ( 6 bits )

-shamt from 6^thbit to 10^thbit ( 5 bits )

-rd from 11^thbit to 15^thbit ( 5 bits )

-rt from 16^thbit to 20^thbit ( 5 bits )

-rs from 21^thbit to 25^thbit ( 5 bits )

-op from 26^thbit to 31^thbit ( 6 bits )

Register type application


a. Non-Jump R -type
               ALU Usage – add rd,rs,rt
b. Jump register
               ALU Usage – jalr rd ,rs
Both:

1. No update beyond the normal increment.
   
2. Source operand fetch: rs and rt.
   
3. ALU operation: determined by the function field.
   
4. Memory access: none.
   
5. Result from ALU write to rd.
   

eg.add, sub,mult,mul, and ,or,jalr ,jr ,sll...
                   
              add $t0 , $t1 , $t2          # $t0 = $t1 + $t2

              sub $t1 , $t2 , $t3          # $t1 = $t2 + $t3
for unsigned value(positive no only) addu,subu, multu...

              addu    $t1 , $t6 , $t7              #  $t1 = $t6 + $t7 
              subu    $t1 , $t6 , $t7              #  $t1 = $t6 + $t7

                                                        
mul $t0,$t0, $t1       same as :         mult       $t0,$t1  
                                                         mfhi       $t0


mfhi - move quantity in special register Hi to $t0:   $t1 = Hi 

Why having hi and lo in multiplication and division?
bacause $t3 and $t4 both is 32 bits quantities, they need 2 registers to store it,put their results in MIPS registers Hi. Similar to division , Hi is remaider , Lo is quotient.
                  div $t1,$t2        # t1 / t2
                  mflo $s0        #s0 = quotient
                  mfhi $s1        #s1 = remainder

Kee Hwaai Sziang B03121067