Slide 5.15: lhu, lbu, and move instructions

lhu, lbu, and move Instructions

The following gives two more load instructions and the move instruction.

lhu rd, mem # load unsigned halfword: Loads the least-significant bits of the destination register with the contents of the halfword that is at the memory location specified by the effective address. Because the machine treats the loaded halfword as an unsigned value, it fills the two most-significant bytes of the destination register with zeros. If the effective address is not even, the machine signals an address error exception.
lbu rd, mem # load unsigned byte: Loads the least-significant byte of the destination register with the contents of the byte that is at the memory location specified by the effective address. Because the machine treats the loaded byte as an unsigned value, it fills the three most-significant bytes of the destination register with zeros.
move rd, rs # move register contents: Moves the contents of source register to the destination register.

lhu lbu & move

`lhu`	`lbu` & `move`
.data val0: .byte 0 val1: .byte 1 val2: .byte 2 .text lhu $a0, val1 li $v0, 1 syscall	.data val0: .byte 0 val1: .byte 1 val2: .byte 2 .text lhu $a0, val0 li $v0, 1 syscall	.data val: .byte -10 .text lbu $t0, val move $a0, $t0 li $v0, 1 syscall
Output	Output	Output

        .data
 val0:  .byte   0
 val1:  .byte   1
 val2:  .byte   2

        .text
        lhu  $a0, val1
        li   $v0, 1
        syscall

        .data
 val0:  .byte   0 
 val1:  .byte   1
 val2:  .byte   2 

        .text 
        lhu  $a0, val0
        li   $v0, 1
        syscall

       .data
 val:  .byte   -10 

       .text 
       lbu   $t0, val
       move  $a0, $t0
       li    $v0, 1
       syscall

Output Output Output

Knock Knock!
Who’s there?
Cash.
Cash who?
I knew you were a nut!