HT82K75R datasheet(20/66 Pages) HOLTEK

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HT82M75R/HT82M75RE

HT82K75R/HT82K75RE

Rev. 1.10

June 11, 2010

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

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.

T i m e r + 2

E x t e r n a l E v e n t

I n c r e m e n t

T i m e r C o u n t e r

T i m e r + 3

T i m e r + 1

Event Counter Mode Timing Chart

+ 1

+ 2

+ 3

+ 4

T i m e r

E x t e r n a l T i m e r

P i n I n p u t

T O N

( w i t h T E = 0 )

f S Y S

I n c r e m e n t

T i m e r C o u n t e r

f S Y S i s s a m p l e d a t e v e r y f a l l i n g e d g e o f T 1 .

Pulse Width Measure Mode Timing Chart

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