Datasheet

© 2009 Microchip Technology Inc. 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
4
4
4