PIC18F2331_07 Datasheet, PDF (156/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
15.3 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 event is selected by control bits, CCP1M3:CCP1M0
(CCP1CON<3:0>). When a capture is made, the
interrupt request flag bit, CCP1IF (PIR1<2>), is set; it
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 captured value.
15.3.1 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.
15.3.2 TIMER1 MODE SELECTION
Timer1 must be running in Timer mode or Synchro-
nized Counter mode to be used with the capture
feature. In Asynchronous Counter mode, the capture
operation may not work.
15.3.3 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.
15.3.4 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. 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 15-1 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 15-1: CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF CCP1CON, F
MOVLW NEW_CAPT_PS
MOVWF CCP1CON
; Turn CCP module off
; Load WREG with the
; new prescaler mode
; value and CCP ON
; Load CCP1CON with
; this value
FIGURE 15-1:
CAPTURE MODE OPERATION BLOCK DIAGRAM
CCP1 Pin
Prescaler
÷ 1, 4, 16
and
Edge Detect
Set Flag bit CCP1IF
CCPR1H CCPR1L
TMR1
Enable
TMR1H
TMR1L
CCP1CON<3:0>
Qs
Set Flag bit CCP2IF
CCP2 Pin
Prescaler
÷ 1, 4, 16
and
Edge Detect
CCP2CON<3:0>
Qs
CCPR2H CCPR2L
TMR1
Enable
TMR1H
TMR1L
DS39616C-page 154
Preliminary
© 2007 Microchip Technology Inc.