PIC16LF877A-I Datasheet, PDF (67/234 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers

8.1 Capture Mode
In Capture mode, CCPR1H:CCPR1L captures the
16-bit value of the TMR1 register when an event occurs
on pin RC2/CCP1. An event is defined as one of the
following:
• Every falling edge
• Every rising edge
• Every 4th rising edge
• Every 16th rising edge
The type of event is configured by control bits,
CCP1M3:CCP1M0 (CCPxCON<3:0>). When a cap-
ture is made, the interrupt request flag bit, CCP1IF
(PIR1<2>), is set. The interrupt flag must be cleared in
software. If another capture occurs before the value in
register CCPR1 is read, the old captured value is
overwritten by the new value.
8.1.1 CCP PIN CONFIGURATION
In Capture mode, the RC2/CCP1 pin should be
configured as an input by setting the TRISC<2> bit.
Note:
If the RC2/CCP1 pin is configured as an
output, a write to the port can cause a
Capture condition.
FIGURE 8-1:
CAPTURE MODE
OPERATION BLOCK
DIAGRAM
RC2/CCP1
pin
Set Flag bit CCP1IF
(PIR1<2>)
Prescaler
÷ 1, 4, 16
CCPR1H
CCPR1L
and
Edge Detect
Capture
Enable
TMR1H
CCP1CON<3:0>
Qs
TMR1L
PIC16F87XA
8.1.2 TIMER1 MODE SELECTION
Timer1 must be running in Timer mode, or Synchro-
nized Counter mode, for the CCP module to use the
capture feature. In Asynchronous Counter mode, the
capture operation may not work.
8.1.3 SOFTWARE INTERRUPT
When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep bit
CCP1IE (PIE1<2>) clear to avoid false interrupts and
should clear the flag bit, CCP1IF, following any such
change in operating mode.
8.1.4 CCP PRESCALER
There are four prescaler settings, specified by bits
CCP1M3:CCP1M0. 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 may
generate an interrupt. Also, the prescaler counter will
not be cleared, therefore, the first capture may be from
a non-zero prescaler. Example 8-1 shows the recom-
mended method for switching between capture
prescalers. This example also clears the prescaler
counter and will not generate the “false” interrupt.
EXAMPLE 8-1:
CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF
MOVLW
MOVWF
CCP1CON
NEW_CAPT_PS
CCP1CON
; Turn CCP module off
; Load the W reg with
; the new prescaler
; move value and CCP ON
; Load CCP1CON with this
; value
 2003 Microchip Technology Inc.
DS39582B-page 65