PIC16F707-ESLASHML datasheet(122/284 Pages) MICROCHIP

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PIC16F707/PIC16LF707

DS41418A-page 122

Preliminary

 2010 Microchip Technology Inc.

16.6.1

TIMERA/B

To select TimerA/B as the timer resource for the

capacitive sensing module:

• Set the TAXCS/TBXCS bit of the CPSACON0/

CPSBCON0 register.

• Clear the TMRACS/TMRBCS bit of the TACON/

TBCON register.

When TimerA/B is chosen as the timer resource, the

capacitive sensing oscillator will be the clock source for

TimerA/B. Refer to Section 14.0 “TimerA/B Mod-

ules” for additional information.

16.6.2

TIMER1/3

To select Timer1/3 as the timer resource for the

capacitive sensing module, set the TMRxCS<1:0> of

the TxCON register to ‘11’. When Timer1/3 is chosen

as the timer resource, the capacitive sensing oscilla-

tor will be the clock source for Timer1/3. Because the

Timer1/3 module has a gate control, developing a

time base for the frequency measurement can be

simplified by using the TimerA/B overflow flag.

It is recommend that the TimerA/B overflow flag, in

conjunction with the Toggle mode of the Timer1/3 gate,

be used to develop the fixed time base required by the

software portion of the capacitive sensing module.

Refer to Section 13.11 “Timer1/3 Control Register ”

for additional information.

16.7

Software Control

The software portion of the capacitive sensing module

is required to determine the change in frequency of the

capacitive sensing oscillator. This is accomplished by

the following:

• Setting a fixed time base to acquire counts on

TimerA/B or Timer1/3.

• Establishing the nominal frequency for the

capacitive sensing oscillator.

• Establishing the reduced frequency for the

capacitive sensing oscillator due to an additional

capacitive load.

• Set the frequency threshold.

16.7.1

NOMINAL FREQUENCY (NO

CAPACITIVE LOAD)

To determine the nominal frequency of the capacitive

sensing oscillator:

• Remove any extra capacitive load on the selected

CPSx pin.

• At the start of the fixed time base, clear the timer

resource.

• At the end of the fixed time base, save the value

in the timer resource.

The value of the timer resource is the number of

oscillations of the capacitive sensing oscillator for the

given time base. The frequency of the capacitive

sensing oscillator is equal to the number of counts on

the timer divided by the period of the fixed time base.

16.7.2

REDUCED FREQUENCY

(ADDITIONAL CAPACITIVE LOAD)

The extra capacitive load will cause the frequency of

the capacitive sensing oscillator to decrease. To

determine the reduced frequency of the capacitive

sensing oscillator:

• Add a typical capacitive load on the selected

CPSx pin.

• Use the same fixed time base as the nominal

frequency measurement.

• At the start of the fixed time base, clear the timer

resource.

• At the end of the fixed time base, save the value

in the timer resource.

The value of the timer resource is the number of

oscillations of the capacitive sensing oscillator with an

additional capacitive load. The frequency of the

capacitive sensing oscillator is equal to the number of

counts on the timer divided by the period of the fixed

time base. This frequency should be less than the

value

obtained

during

the

nominal

frequency

measurement.

TABLE 16-3:

TIMER1/3 ENABLE FUNCTION

TMRxON

TMRxGE

Timerx Operation

Off

Count Enabled by Input

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