Timer Program Example - Holtek HT45F23A Manual

HT45F23A/HT45F24A
TinyPower Flash MCU with OPA & Comparators
TM
When the Timer/Event counter overflows, its corresponding interrupt request flag in the interrupt
control register will be set. If the timer interrupt is enabled this will in turn generate an interrupt
signal. However irrespective of whether the interrupts are enabled or not, a Timer/Event counter
overflow will also generate a wake-up signal if the devices are in a Power-down condition. This
situation may occur if the Timer/Event Counter is in the Event Counting Mode and if the external
signal continues to change state. In such a case, the Timer/Event Counter will continue to count
these external events and if an overflow occurs the devices will be woken up from its Power-down
condition. To prevent such a wake-up from occurring, the timer interrupt request flag should first be
set high before issuing the HALT instruction to enter the Power Down Mode.

Timer Program Example

This program example shows how the Timer/Event Counter registers are setup, along with how the
interrupts are enabled and managed. Note how the Timer/Event Counter is turned on, by setting bit
4 of the Timer Control Register. The Timer/Event Counter can be turned off in a similar way by
clearing the same bit. This example program sets the Timer/Event Counter to be in the timer mode,
which uses the internal system clock as the clock source.
org 04h
org 0ch
jmp tmrint
:
org 20h
:
tmrint:
:
reti:
:
begin:
mov a,09bh
mov tmr0,a;
mov a,081h
mov tmr0c,a
mov a,009h
mov intc0,a
set tmr0c.4
Rev. 1.40
; external interrupt vector
; Timer/Event Counter 0 interrupt vector
; jump here when the Timer/Event Counter 0 overflows
; main program
; internal Timer/Event Counter 0 interrupt routine
; Timer/Event Counter 0 main program placed here
; setup Timer 0 registers
; setup Timer 0 preload value
; setup Timer 0 control register
; timer mode and prescaler set to /2
; setup interrupt register
; enable master interrupt and timer interrupt
; start Timer/Event Counter 0 - note mode bits must be previously
; setup
73 March 29, 2019