.386
.model flat,stdcall
option casemap:none
include \masmplus\include\windows.inc
include \masmplus\include\kernel32.inc
includelib \masmplus\lib\kernel32.lib
include \masmplus\include\user32.inc
includelib \masmplus\lib\user32.lib

.data
MsgBoxCaption  db "结果！",0
MsgBoxText    db 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
.code
start:
mov  al,97h
call  ShowAL


invoke MessageBox, NULL, addr MsgBoxText, addr MsgBoxCaption, MB_YESNOCANCEL
invoke ExitProcess, NULL

ShowAL proc
        mov  dl,al      ;保存AL
        mov  cl,04      
        shr  al,cl      ;AL高4位移至低4位
        mov  cx,02h      ;循环2次
        xor  ebx,ebx
        mov  esi,offset MsgBoxText

Low4bit:
cmp  al,09
        jbe  larger    ;低4位超过9
        add  al,07
larger:   
add  al,30h

        mov  [esi],al
        inc  esi      
        
        mov  al,dl      ;恢复保存
          and  al,0Fh
          loop  Low4bit
        
        ret
ShowAL  endp

end start
显示AL中的数值，但是程序在运行期会出现错误

程序只要对了就行 了