PIC16F882-I Datasheet, PDF (128/328 Pages) Microchip Technology – 28/40/44-Pin, Enhanced Flash-Based 8-Bit CMOS Microcontrollers

PIC16F882/883/884/886/887
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.
Note:
If the CCPx pin is configured as an output,
a write to the port can cause a capture
condition.
FIGURE 11-1:
CAPTURE MODE
OPERATION BLOCK
DIAGRAM
CCPx
pin
Set Flag bit CCPxIF
Prescaler ^{(PIRx register)}
÷ 1, 4, 16
CCPRxH
CCPRxL
and
Edge Detect
Capture
Enable
CCPxCON<3:0>
System Clock (FOSC)
TMR1H
TMR1L
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
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
DS41291F-page 126
© 2009 Microchip Technology Inc.