INT 1cH: User Timer Interrupt
This vector (0:0070) is taken by BIOS upon each tick of the hardware clock
(every 55ms; approximately 18.2 times per second). It initially points to
a dummy IRET, but may be changed by a user program to point to a timer-
based background task.
Since INT 1cH is executed during the lower hardware-based timer interrupt
(IRQ 0), you must remember that the system has not yet reset the interrupt
controller. Therefore other hardware interrupts, notably the keyboard
interrupt, will not occur while INT 1cH is in progress (you can't get user
Most TSR popup programs prefer to intercept the lower-level INT 08H
vector, call the original vector, then perform the timer-based operation
after BIOS has finished its housekeeping chores.
See INT 08H for suggestions and recommendations.
See Also: Terminate and Stay Resident (TSR)