运行代码时，出现最小值错误，如何修复？

.data
prompt: .asciiz "Enter your first and last name: "
max_msg: .asciiz "\nMaximum ASCII value: "
min_msg: .asciiz "\nMinimum ASCII value: "
newline: .asciiz "\n"

.text
.globl main

main:
    # Prompt for input
    li $v0, 4       # system call for print string
    la $a0, prompt  # load address of prompt
    syscall

    # Read input
    li $v0, 8       # system call for read string
    la $a0, buffer  # load address of buffer
    li $a1, 255     # set maximum length of input
    syscall

    # Find maximum and minimum ASCII values
    la $t0, buffer   # load address of buffer into $t0

    li $t1, 0x20     # initialize $t1 to the ASCII value of space
    li $t2, 0x7F     # initialize $t2 to the largest possible ASCII value
    li $t3, 0x00     # initialize $t3 to the smallest possible ASCII value
    li $t4, 0         # initialize $t4 to 0

loop:
    lb $t5, ($t0)    # load byte from current position
    beq $t5, 0, done # if byte is null terminator, we're done

    # if byte is a space, skip it
    beq $t5, $t1, next

    # if this is the first non-space character, initialize $t4
    beq $t4, 0, init

    # find maximum ASCII value
    bgt $t5, $t3, is_max
    j is_min

is_max:
    move $t3, $t5    # set $t3 to current byte
    j next

    # find minimum ASCII value
is_min:
    blt $t5, $t2, set_min
    j next

set_min:
    move $t2, $t5    # set $t2 to current byte
    j next

init:
    # initialize $t4 to the first non-space character
    move $t4, $t5
    j next

next:
    addi $t0, $t0, 1 # move to next byte
    j loop           # jump to loop

done:
    # Print results
    li $v0, 4         # system call for print string
    la $a0, max_msg   # load address of max message
    syscall

    li $v0, 1         # system call for print integer
    move $a0, $t3     # load maximum ASCII value
    syscall

    li $v0, 4         # system call for print string
    la $a0, min_msg   # load address of min message
    syscall

    li $v0, 1         # system call for print integer
    move $a0, $t2     # load minimum ASCII value
    syscall

    li $v0, 4         # system call for print string
    la $a0, newline   # load address of newline
    syscall

    # Exit program
    li $v0, 10        # set system call number to 10 for exit
    syscall           # perform system call to exit
.data
buffer: .space 256   # allocate space for input buffer

这里我的名字的最大ascii值是正确的，但最小值是错误的。

我的输出：

输入您的名字和姓氏：Isaac Newton最大ASCII值：119最小ASCII值：10

我的预期输出：

输入您的名字和姓氏：Isaac Newton最大ASCII值：119最小ASCII值：73
我该怎么解决？