Slide 5.18: sw, sh, and sb instructions

sw, sh, and sb Instructions

The store instruction copies data from a register to memory and the register is not changed when its data is copied to memory. The following gives three store instructions.

sw rd, mem # store word: Stores the contents of a word from the source register in the memory location specified by the effective address. The effective address must be divisible by four, otherwise the machine signals an address error exception.
sh rd, mem # store halfword: Stores the two least-significant bytes of the source register in the halfword that is at the memory location specified by the effective address. The effective address must be divisible by two, otherwise the machine signals an address error exception.
sb rd, mem # store byte: Stores the contents of the source register’s least-significant byte in the byte specified by the effective address.

sw sh sb

`sw`	`sh`	`sb`
.data X: .word 1 .byte 2 Y: .word 3 .text li $t0, 1 sw $t0, X+4 lw $a0, Y li $v0, 1 syscall	.data X: .byte 1 Y: .half 2 .text li $t0, 1 sh $t0, X+2 lh $a0, Y li $v0, 1 syscall	.data s: .asciiz "abc" .text li $t0, 'd' # 'd': character d sb $t0, s+2 la $a0, s li $v0, 4 syscall
Output	Output	Output

     .data
 X:  .word  1
     .byte  2
 Y:  .word  3

     .text 
     li  $t0, 1
     sw  $t0, X+4
     lw  $a0, Y
     li  $v0, 1
     syscall

     .data
 X:  .byte  1
 Y:  .half  2

     .text 
     li  $t0, 1
     sh  $t0, X+2
     lh  $a0, Y
     li  $v0, 1
     syscall

     .data
 s:  .asciiz  "abc"

     .text 
     li  $t0, 'd'
 # 'd': character d
     sb  $t0, s+2
     la  $a0, s
     li  $v0, 4
     syscall

Output Output Output