Microchip Technology AC244045 Data Sheet

DS41440C-page 214

 2010-2012 Microchip Technology Inc.

The Capture mode function described in this section is
available and identical for CCP modules ECCP1,
ECCP2, CCP3 and CCP4.
Capture mode makes use of the 16-bit Timer1
resource. When an event occurs on the CCPx pin, the
16-bit CCPRxH:CCPRxL register pair captures and
stores the 16-bit value of the TMR1H:TMR1L register
pair, respectively. An event is defined as one of the
following and is configured by the CCPxM<3:0> bits of
the CCPxCON 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.

 shows a simplified diagram of the Capture

operation.

24.1.1

CCP PIN CONFIGURATION

In Capture mode, the CCPx pin should be configured
as an input by setting the associated TRIS control bit.
Also, the CCPx pin function can be moved to
alternative pins using the APFCON0 or APFCON1
register. Refer to 

 for more details.

24.1.2

TIMER1 MODE RESOURCE

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. 
See 

for more information on configuring Timer1.

24.1.3

SOFTWARE INTERRUPT MODE

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.

24.1.4

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. 

 demonstrates the code to

perform this function.

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

CCPxM<3:0>

Prescaler
 1, 4, 16

and

Edge Detect

pin

CCPx

System Clock (F

OSC

)

Clocking Timer1 from the system clock
(F

OSC

) should not be used in Capture

mode. In order for Capture mode to
recognize the trigger event on the CCPx
pin, Timer1 must be clocked from the
instruction clock (F

OSC

/4) or from an

external clock source.

BANKSEL CCPxCON

;Set Bank bits to point
;to CCPxCON

CLRF

CCPxCON

;Turn CCP module off

MOVLW

NEW_CAPT_PS ;Load the W reg with

;the new prescaler
;move value and CCP ON

MOVWF

CCPxCON

;Load CCPxCON with this
;value