HT82K75R datasheet(21/66 Pages) HOLTEK

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HT82M75R/HT82M75RE

HT82K75R/HT82K75RE

Rev. 1.30

November 24, 2010

I/O Interfacing

The Timer/Event Counter, when configured to run in the

event counter or pulse width measurement mode, re-

quire the use of the external PA2 pin for correct opera-

tion. As this pin is a shared pin it must be configured

correctly to ensure it is setup for use as a Timer/Event

Counter input and not as a normal I/O pin. This is imple-

mented by ensuring that the mode select bits in the

Timer/Event Counter control register, select either the

event counter or pulse width measurement mode. Addi-

tionally the Port Control Register PAC bit 2 must be set

high to ensure that the pin is setup as an input. Any

pull-high resistor configuration option on this pin will re-

main valid even if the pin is used as a Timer/Event

Counter input.

Programming Considerations

When configured to run in the timer mode, the internal

system clock is used as the timer clock source and is

therefore synchronised 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-

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 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 prop-

erly initialised before using them for the first time. The

associated timer interrupt enable bits in the interrupt

control register must be properly set otherwise the inter-

nal interrupt associated with the timer will remain inac-

tive. The edge select, timer mode and clock source

control bits in timer control register must also be cor-

rectly 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 un-

known. 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 af-

ter the timer mode bits have been properly setup. Set-

ting the timer enable bit high together with a mode bit

modification, may lead to improper timer operation if ex-

ecuted as a single timer control register byte write in-

struction.

When the Timer/Event counter overflows, its corre-

sponding interrupt request flag in the interrupt control

will in turn generate an interrupt signal. But the timer for

internal clock overflow can

¢t wake up the MCU if MCU is

in a Power down condition.

HT82K75R 数据表(PDF) 21 Page - Holtek Semiconductor Inc

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