PIC16F72-E Datasheet, PDF (40/136 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontoller with A/D Converter

PIC16F72
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 CCP1M3:CCP1M0
(CCP1CON<3:0>). When a capture is made, the inter-
rupt 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.
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 is configured as an out-
put, 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
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 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. 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 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
MOVLW
MOVWF
CCP1CON
NEW_CAPT_PS
CCP1CON
; Turn CCP module off
; Load the W reg with
; the new prescaler
; mode value and CCP ON
; Load CCP1CON with
; this value
DS39597C-page 38
© 2007 Microchip Technology Inc.