ht82k75rew Holtek Semiconductor Inc., ht82k75rew Datasheet - Page 23

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

Configuring the Event Counter Mode
In this mode, a number of externally changing logic
events, occurring on external pin PA2/TMR, can be re-
corded by the internal timer. For the timer to operate in
the event counting mode, bits TM1 and TM0 of the
TMRC register must be set to 0 and 1 respectively. The
timer-on bit, TON must be set high to enable the timer to
count. With TE low, the counter will increment each time
the PA2/TMR pin receives a low to high transition. If the
TE bit is high, the counter will increment each time
PA2/TMR receives a high to low transition. As in the
case of the other two modes, when the counter is full
and overflows, the timer will be reset to the value al-
ready loaded into the preload register and continue
counting. If the timer interrupt is enabled, an interrupt
signal will also be generated. The timer interrupt can be
disabled by ensuring that the ETI bit in the INTC register
is cleared to zero. To ensure that the external pin
PA2/TMR is configured to operate as an event counter
input pin, two things have to happen. The first is to en-
sure that the TM0 and TM1 bits place the timer/event
counter in the event counting mode, the second is to en-
sure that the port control register configures the pin as
an input. In the Event Counting mode, the Timer/Event
Counter will continue to record externally changing logic
events on the timer input pin, even if the microcontroller
is in the Power Down Mode.
Configuring the Pulse Width Measurement Mode
In this mode, the width of external pulses applied to the
pin-shared external pin PA2/TMR can be measured. In
the Pulse Width Measurement Mode, the timer clock
source is supplied by the internal clock. For the timer to
operate in this mode, bits TM0 and TM1 must both be
set high. If the TE bit is low, once a high to low transition
has been received on the PA2/TMR pin, the timer will
Rev. 1.00
Pulse Width Measure Mode Timing Chart
Event Counter Mode Timing Chart
23
start counting until the PA2/TMR pin returns to its origi-
nal high level. At this point the TON bit will be automati-
cally reset to zero and the timer will stop counting. If the
TE bit is high, the timer will begin counting once a low to
high transition has been received on the PA2/TMR pin
and stop counting when the PA2/TMR pin returns to its
original low level. As before, the TON bit will be automat-
ically reset to zero and the timer will stop counting. It is
important to note that in the Pulse Width Measurement
Mode, the TON bit is automatically reset to zero when
the external control signal on the external timer pin re-
turns to its original level, whereas in the other two
modes the TON bit can only be reset to zero under pro-
gram control. The residual value in the timer, which can
now be read by the program, therefore represents the
length of the pulse received on pin PA2/TMR. As the
TON bit has now been reset any further transitions on
the PA2/TMR pin will be ignored. Not until the TON bit is
again set high by the program can the timer begin fur-
ther pulse width measurements. In this way single shot
pulse measurements can be easily made. It should be
noted that in this mode the counter is controlled by logi-
cal transitions on the PA2/TMR pin and not by the logic
level.
As in the case of the other two modes, when the counter
is full and overflows, the timer will be reset to the value
already loaded into the preload register. If the timer in-
terrupt is enabled, an interrupt signal will also be gener-
ated. To ensure that the external pin PA2/TMR is
configured to operate as a pulse width measuring input
pin, two things have to happen. The first is to ensure that
the TM0 and TM1 bits place the timer/event counter in
the pulse width measuring mode, the second is to en-
sure that the port control register configures the pin as
an input.
HT82M75REW/HT82K75REW
June 11, 2010