PIC16F872 Datasheet, PDF (48/160 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontroller

PIC16F872
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:
• Every falling edge
• Every rising edge
• Every 4th rising edge
• Every 16th rising edge
An event is selected by control bits CCP1M<3:0>
(CCP1CON<3:0>). When a capture is made, the inter-
rupt 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 will be lost.
8.1.1 CCP PIN CONFIGURATION
In Capture mode, the RC2/CCP1 pin should be config-
ured 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 cap-
ture condition.
FIGURE 8-1: CAPTURE MODE OPERATION
BLOCK DIAGRAM
RC2/CCP1
Pin
Set flag bit CCP1IF
Prescaler
(PIR1<2>)
÷ 1, 4, 16
CCPR1H
and
edge detect
Capture
Enable
CCP1CON<3:0>
Q’s
TMR1H
CCPR1L
TMR1L
8.1.2 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.
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
CCP1M<3:0>. Whenever the CCP module is turned off,
or the CCP module is not in capture mode, the pres-
caler counter is cleared. Any reset will clear the pres-
caler 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 pres-
calers. This example also clears the prescaler counter
and will not generate the “false” interrupt.
EXAMPLE 8-1: CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF CCP1CON
;Turn CCP module off
MOVLW NEW_CAPT_PS ;Load the W reg with
; the new precscaler
; move value and CCP ON
MOVWF CCP1CON
;Load CCP1CON with this
; value
DS30221A-page 48
Preliminary
© 1999 Microchip Technology Inc.