HT46R0664 datasheet(52/92 Pages) HOLTEK

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HT46R0664

Enhanced A/D+LCD Type 8-Bit OTP MCU

result in a counting error, this should be taken into account by the programmer. Care must be taken

to ensure that the timers are properly initialised before using them for the first time. The associated

timer enable bits in the interrupt control register must be properly set otherwise the internal interrupt

associated with the timer will remain inactive. The edge select, timer mode and clock source control

bits in timer control register must also be correctly set to ensure the timer is properly configured

for the required application. It is also important to ensure that an initial value is first loaded into

the timer registers before the timer is switched on; this is because after power-on the initial values

of the timer registers are unknown. After the timer has been initialized the timer can be turned on

and off by controlling the enable bit in the timer control register. When the Timer/Event Counter

overflows, its corresponding interrupt request flag in the interrupt control register will be set. If the

Timer/Event Counter 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 device is 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 device 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 Idle/Sleep Mode.

Timer Program Example

The program 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 Counters to be in the timer mode, which uses

the internal system clock as their clock source.

PFD Programming Example

org 04h

; external interrupt vector

org 08h

; Timer Counter 0 interrupt vector

jmp tmr0int

; jump here when Timer 0 overflows

org 20h

; main program

;internal Timer 0 interrupt routine

tmr0int:

;Timer 0 main program placed here

begin:

;setup Timer 0 registers

mov a,09bh

; setup Timer 0 preload value

mov tmr0,a

mov a,081h

; setup Timer 0 control register

mov tmr0c,a

; timer mode and prescaler set to /2

;setup interrupt register

mov a,00dh

; enable master interrupt and both timer interrupts

mov intc0,a

set tmr0c.4

; start Timer 0

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