HT46R46E datasheet(29/73 Pages) HOLTEK

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HT46R46E/C46E/R47E/C47E/R48AE/C48AE/R49E

Rev. 1.20

August 15, 2007

Programming Considerations

When configured to run in the timer mode, the internal

system clock is used as the timer clock source and is

therefore synchronized with the overall operation of the

microcontroller. In this mode when the appropriate timer

nal interrupt signal directing the program flow to the re-

spective internal interrupt vector. For the pulse width

measurement mode, the internal system clock is also

used as the timer clock source but the timer will only run

when the correct logic condition appears on the external

timer input pin. As this is an external event and not syn-

chronized with the internal timer clock, the

microcontroller will only see this external event when the

next timer clock pulse arrives. As a result, there may be

small differences in measured values requiring pro-

grammers to take this into account during programming.

The same applies if the timer is configured to be in the

event counting mode, which again is an external event

and not synchronized with the internal system or timer

clock.

When the Timer/Event Counter is read, or if data is writ-

ten to the preload register, the clock is inhibited to avoid

errors, however as this may 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 in-

itialised before using them for the first time. The associ-

ated 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 regis-

ter must also be correctly set to ensure the timer is prop-

erly 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 reg-

isters are unknown. After the timer has been initialised

the timer can be turned on and off by controlling the en-

able bit in the timer control register. Note that setting the

timer enable bit high to turn the timer on, should only be

executed after the timer mode bits have been properly

setup. Setting the timer enable bit high together with a

mode bit modification, may lead to improper timer oper-

ation if executed as a single timer control register byte

write instruction

When the Timer/Event counter overflows, its corre-

sponding interrupt request flag in the interrupt control

will in turn generate an interrupt signal. However irre-

spective 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 condi-

tion. 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 exter-

nal 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 re-

quest 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 inter-

rupts 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

; external interrupt vector

reti

org 08h

; Timer/Event Counter interrupt vector

jmp tmrint

; jump here when Timer overflows

org 20h

; main program

;internal Timer/Event Counter interrupt routine

tmrint:

; Timer/Event Counter main program placed here

reti

begin:

;setup Timer registers

mov a,09bh

; setup Timer preload value

mov tmr,a;

mov a,081h

; setup Timer control register

mov tmrc,a

; timer mode and prescaler set to /2

; setup interrupt register

mov a,005h

; enable master interrupt and timer interrupt

mov intc,a

set tmrc.4

; start Timer - note Mode bits must be previously setup

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