INT 1Ch (28)             User Timer Tick

    Called at every timer tick (18.2 times per second, or every 55 ms) by
    INT 08h (System Timer).

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    By default, the interrupt handler for this interrupt IRETs back to the
    caller. The user can supply his own handler so he can attain control
    at every timer tick.

       Notes:         Note that this interrupt is called by the hardware
                      timer interrupt (INT 08h), which has not signaled
                      the end of the interrupt back to the interrupt
                      controller. Therefore, this routine is limited in
                      the actions it can take, since all interrupts will
                      be disabled. A better approach to this problem is to
                      intercept INT 08h. The new INT 08h handler will
                      first call the standard INT 08h, which will handle
                      the interrupt controller completion signals
                      mentioned above. Then after the standard INT 08h is
                      completed, the new handler can do whatever it has to
                      do at every timer tick.