PIC16F882-I datasheet(128/328 Pages) MICROCHIP

128 / 328 page

PIC16F882/883/884/886/887

DS41291F-page 126

11.3

Capture Mode

In Capture mode, the CCPRxH, CCPRxL register pair

captures the 16-bit value of the TMR1 register when an

event occurs on pin CCPx. An event is defined as one

of the following and is configured by the CCP1M<3:0>

bits of the CCP1CON register:

• Every falling edge

• Every rising edge

• Every 4th rising edge

• Every 16th rising edge

When a capture is made, the Interrupt Request Flag bit

CCPxIF of the PIRx register is set. The interrupt flag

must be cleared in software. If another capture occurs

before the value in the CCPRxH, CCPRxL register pair

is read, the old captured value is overwritten by the new

captured value (see Figure 11-1).

11.3.1

CCP PIN CONFIGURATION

In Capture mode, the CCPx pin should be configured

as an input by setting the associated TRIS control bit.

FIGURE 11-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

11.3.2

TIMER1 MODE SELECTION

Timer1 must be running in Timer mode or Synchronized

Counter mode for the CCP module to use the capture

feature. In Asynchronous Counter mode, the capture

operation may not work.

11.3.3

SOFTWARE INTERRUPT

When the Capture mode is changed, a false capture

interrupt may be generated. The user should keep the

CCPxIE interrupt enable bit of the PIEx register clear to

avoid false interrupts. Additionally, the user should

clear the CCPxIF interrupt flag bit of the PIRx register

following any change in Operating mode.

11.3.4

CCP PRESCALER

There are four prescaler settings specified by the

CCPxM<3:0> bits of the CCPxCON register. Whenever

the CCP module is turned off, or the CCP module is not

in Capture mode, the prescaler counter is cleared. Any

Reset will clear the prescaler counter.

Switching from one capture prescaler to another does not

clear the prescaler and may generate a false interrupt. To

avoid this unexpected operation, turn the module off by

clearing the CCPxCON register before changing the

prescaler (see Example 11-1).

EXAMPLE 11-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note:

If the CCPx pin is configured as an output,

a write to the port can cause a capture

condition.

CCPRxH

CCPRxL

TMR1H

TMR1L

Set Flag bit CCPxIF

(PIRx register)

Capture

Enable

CCPxCON<3:0>

Prescaler

÷ 1, 4, 16

and

Edge Detect

CCPx

System Clock (FOSC)

BANKSEL CCP1CON

;Set Bank bits to point

;to CCP1CON

CLRF

CCP1CON

;Turn CCP module off

MOVLW

NEW_CAPT_PS ;Load the W reg with

; the new prescaler

; move value and CCP ON

MOVWF

CCP1CON

;Load CCP1CON with this

; value

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