PIC18F44J10 datasheet(131/368 Pages) MICROCHIP

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DS39682E-page 129

PIC18F45J10 FAMILY

14.2

Capture Mode

In Capture mode, the CCPRxH:CCPRxL register pair

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

event occurs on the corresponding CCPx pin. An event

is defined as one of the following:

• every falling edge

• every rising edge

• every 4th rising edge

• every 16th rising edge

The event is selected by the mode select bits,

CCPxM<3:0> (CCPxCON<3:0>). When a capture is

made, the interrupt request flag bit, CCPxIF, is set; it

must be cleared in software. If another capture occurs

before the value in register CCPRx is read, the old

captured value is overwritten by the new captured value.

14.2.1

CCP PIN CONFIGURATION

In Capture mode, the appropriate CCPx pin should be

configured as an input by setting the corresponding

TRIS direction bit.

14.2.2

SOFTWARE INTERRUPT

When the Capture mode is changed, a false capture

interrupt may be generated. The user should keep the

CCPxIE interrupt enable bit clear to avoid false inter-

rupts. The interrupt flag bit, CCPxIF, should also be

cleared following any such change in operating mode.

14.2.3

CCP PRESCALER

There are four prescaler settings in Capture mode; they

are specified as part of the operating mode selected by

the mode select bits (CCPxM<3:0>). Whenever the

CCP module is turned off or Capture mode is disabled,

the prescaler counter is cleared. This means that any

Reset will clear the prescaler counter.

Switching from one capture prescaler to another may

generate an interrupt. Also, the prescaler counter will

not be cleared; therefore, the first capture may be from

a non-zero prescaler. Example 14-1 shows the

recommended method for switching between capture

prescalers. This example also clears the prescaler

counter and will not generate the “false” interrupt.

EXAMPLE 14-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

(CCP2 SHOWN)

FIGURE 14-1:

CAPTURE MODE OPERATION BLOCK DIAGRAM

Note:

If RB3/CCP2 or RC1/CCP2 is configured

as an output, a write to the port can cause

a capture condition.

CLRF

CCP2CON

; Turn CCP module off

MOVLW

NEW_CAPT_PS

; Load WREG with the

; new prescaler mode

; value and CCP ON

MOVWF

CCP2CON

; Load CCP2CON with

; this value

CCPR1H

CCPR1L

TMR1H

TMR1L

Set CCP1IF

Q1:Q4

CCP1CON<3:0>

CCP1 pin

Prescaler

÷ 1, 4, 16

and

Edge Detect

CCPR2H

CCPR2L

TMR1H

TMR1L

Set CCP2IF

CCP2CON<3:0>

CCP2 pin

Prescaler

÷ 1, 4, 16

and

Edge Detect

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