HT45FM03B(2009) 查看數據表（PDF） - Holtek Semiconductor

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HT45FM03B
(Rev.:2009)

Brushless DC Motor Flash Type 8-Bit MCU

Holtek Semiconductor 

HT45FM03B

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 register is full, the microcontroller will generate an

internal interrupt signal directing the program flow to the

respective 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-

chronised 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 synchronised with the internal system or timer

clock.

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

ten to the registers, 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 as-

sociated 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 register before the timer is

switched on; this is because after power-on the initial

value of the timer register is unknown. After the timer

has been initialised the timer can be turned on and off by

controlling the enable 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 operation 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

register will be set. If the timer interrupt is enabled this

will in turn generate an interrupt signal. However irre-

spective of whether the timer interrupt is 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.

Rev. 1.00

29

December 16, 2009

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