MIPS汇编字符输入

Question

我遇到了这个问题，试图在MIPS Assembly中获取用户的char输入。 我似乎不明白为什么，当输入一个字符时，不需要按ENTER键，而当输入任何其他类型，如.word时，你总是要按ENTER键。你可以向我解释一下，并告诉我在代码中我做错了什么吗？谢谢。

以下是相关代码：

.data
message:  .asciiz "Please, enter the number of steps: \n"
message2: .asciiz "The factorial is: \n"
cont:     .asciiz "Do you want to continue? (Y or N) \n"
yes:      .byte 'Y'
no:       .byte 'N'
.text
main:

# $t1 contains the iterating number
addi $t1, $zero, 1

# $t3 contains the factorial
addi $t3, $zero, 1

# set $t2 which is the number we want a factorial for to 0
add $t2, $zero, $zero

# now $t5 contains 'Y' and $t6 contains 'N'
lb $t5, yes
lb $t6, no

while:
# show the message
li $v0, 4
la $a0, message
syscall

# read the number
li $v0, 5
syscall

# $t2 contains the condition for the loop, which is the number we want a factorial for
add  $t2, $t2, $v0

for:
    # while $t1 is less than $t2 do
    bgt  $t1, $t2, end
    # $t3 = $t3 * $t1
    mul  $t3, $t3, $t1
    # $t1++
    addi $t1, $t1, 1
    # jump at the start of the loop
    j for

end:
    # prints "Do you want to continue?"
    li $v0, 4
    la $a0, cont
    syscall

    # reads a character
    li $v0, 12
    syscall

    # if the answer is yes, jump to the start of the while loop
    beq $v0, $t5, while

    # if no, show the result
    beq $v0, $t6, show

    # else ask another time
    j end

show:
    # prints out the message
    li   $v0, 4
    la   $a0, message2
    syscall
    # prints out the result
    li   $v0, 1
    add  $a0, $zero, $t3
    syscall

# end of the main function
li $v0, 10
syscall