用汇编编写DOS下的内存驻留程序(3)：中断矢量

p; push    si
    push    dx                      ;Save low nybble temporarily
    push    cx                      ;Save CX
    mov     cl,4                    ;Set shift count to 4
    shr     dx,cl                   ;Shift high nybble into low nybble
    and     dx,0fh                  ;Mask out all but low nybble
    mov     si,dx                   ;Use low nybble as index into
    mov     al,hextab[si]           ;hexadecimal character table
    call    dchar                   ;Display character
    pop     cx                      ;Restore CX
    pop     dx                      ;Restore low nybble
    and     dx,0fh                  ;Mask out all but low nybble
    mov     si,dx                   ;Use low nybble as an index into
    mov     al,hextab[si]           ;hexadecimal character table
    call    dchar                   ;Display character
    pop     si                      ;Restore registers
    pop     dx
    pop     ax
    ret
   dbyte   endp
   ;----------------------------------------------------------------------