TITLE TIMER_TICK
;timer interrupt procedure
     EXTRN TIMER_FLAG:BYTE
     PUBLIC TIMER_TICK
.MODEL SMALL
.CODE
;timer routine
TIMER_TICK PROC
;save registers
     PUSH DS                    ;save DX
     PUSH AX
     MOV  AX,SEG TIMER_FLAG     ;get segment of flag
     MOV DS,AX                  ;put in DS
     MOV TIMER_FLAG,1           ;set flag
;restor regesters
     POP AX
     POP DX                     ;restor DS
     IRET
TIMER_TICK ENDP                 ;end timer routine
     END

