PIC18F2331 Datasheet, PDF (155/396 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 is configured as an out-
put, a write to the port can cause a capture
condition.
15.3.2 TIMER1 MODE SELECTION
Timer 1 must be running in Timer mode or Synchro-
nized Counter mode to be used with the capture fea-
ture. 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 pres-
calers. 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>
Q’s
Set Flag bit CCP2IF
CCP2 pin
Prescaler
÷ 1, 4, 16
and
Edge Detect
CCP2CON<3:0>
Q’s
CCPR2H CCPR2L
TMR1
Enable
TMR1H
TMR1L
 2003 Microchip Technology Inc.
Preliminary
DS39616B-page 153