我们可以使用系统调用code为读字，这应该是系统调用code 12，则字符（二进制ASCII code）的被存储在$ V0。然后，你可以做一个寄存器等于121，另一个是110，如果相等，则分支。

One can use the system call code for Read Character, which should be system call code 12, then the character (binary ASCII code) will be stored in $v0. Then you can make a register equal to 121 and another to 110. Then branch if equal.

SPIM系统调用codeS：
http://www.doc.ic.ac.uk/lab /secondyear/spim/node8.html

SPIM system call codes: http://www.doc.ic.ac.uk/lab/secondyear/spim/node8.html