Техническая Спецификация для Microchip Technology ARD00385

 2009-2011 Microchip Technology Inc.

DS39957D-page 243

18.2.3

SOFTWARE INTERRUPT

When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep the
CCP4IE bit (PIE4<1>) clear to avoid false interrupts
and should clear the flag bit, CCP4IF, following any
such change in operating mode.

18.2.4

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 (CCP4M<3:0>).
Whenever the CCP module is turned off, or the CCP
module is not in Capture mode, 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. Doing that also will not clear the
prescaler counter – meaning the first capture may be
from a non-zero prescaler.

 shows the recommended method for

switching between capture prescalers. This example
also clears the prescaler counter and will not generate
the “false” interrupt.

Set CCP5IF

TMR5
Enable

Q1:Q4

CCP5CON<3:0>

CCP5 Pin

Prescaler
 1, 4, 16

and

Edge Detect

TMR1
Enable

C5TSEL0

C5TSEL0

Set CCP4IF

TMR3
Enable

CCP4CON<3:0>

CCP4 Pin

Prescaler
 1, 4, 16

TMR1
Enable

C4TSEL0
C4TSEL1

C4TSEL0

C4TSEL1

and

Edge Detect

4

4

4

This block diagram uses CCP4 and CCP5, and their appropriate timers, as an example. For details on all
of the CCP modules and their timer assignments, see 

 and 

CLRF

CCP4CON

; Turn CCP module off

MOVLW NEW_CAPT_PS

; Load WREG with the

; new prescaler mode

; value and CCP ON

MOVWF CCP4CON

; Load CCP4CON with

; this value