MIPS Assembly convert integer to ascii string using memory

Hi i have a problem with my subroutine code. here is my code. It's giving a

Runtime exception at 0x00400074: address out of range 0x000000c8 error.

The line is: sb $t2, 0($t4) - It's the second store byte.

intToa: addi    $sp, $sp, -12
    sw  $ra ,8($sp)
    sw  $a0, 4($sp)
    sw  $a1, 0($sp)

    move    $t0, $a0        
    move    $t4, $a1        

    bne $t0, $zero, while                           
    li  $t2, 48         
    sb  $t2, 0($t4)
    addi    $t4, $t4, 1 
    b   end 

 while:     beq $t0, $zero, end
    li  $t6, 10         
    div $t0, $t6        # divide $t0 by 10
    mfhi    $t1         # $t3 = $t0%10 (last digit of $t0)
    mflo    $t0         # $t0 = $t0/10 (first digit of $t0)

    addi    $t2, $t1, 48        # store character '0' to $t1 in
    sb  $t2, 0($t4)             # out destinationg string


    addi    $t4, $t4, 1     # increment our string pointer
    j   while               # continue looping

 end:
    sb  $zero, 0($t4)       # null terminate our string
    move    $a1, $a0        
    jal reverse
    lw  $ra, 12($sp)

    addiu   $sp, $sp, 12        # put stack back in place
    jr  $ra