ht82k75rew Holtek Semiconductor Inc., ht82k75rew Datasheet - Page 24

• Manufacturer Part Number: ht82k75rew
• Description: Ht82m75rew/ht82k75rew 2.4ghz Transceiver 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

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
register is full, the microcontroller will generate an inter-
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-
c h ro n i se d wi th the i nterna l ti me r c lo ck, 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.
Rev. 1.00
24
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
register will be set. If the timer interrupt is enabled this
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.
HT82M75REW/HT82K75REW
June 11, 2010