PIC16LF720_11 Datasheet, PDF (110/244 Pages) Microchip Technology – 20-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC16(L)F720/721
15.1 Capture Mode
In Capture mode, CCPR1H:CCPR1L captures the
16-bit value of the TMR1 register when an event occurs
on pin CCP1. An event is defined as one of the
following and is configured by the CCP1M<3:0> bits of
the CCP1CON register:
• Every falling edge
• Every rising edge
• Every 4th rising edge
• Every 16th rising edge
When a capture is made, the Interrupt Request Flag bit
CCP1IF of the PIR1 register is set. The interrupt flag
must be cleared in software. If another capture occurs
before the value in the CCPR1H, CCPR1L register pair
is read, the old captured value is overwritten by the new
captured value (refer to Figure 15-1).
15.1.1 CCP1 PIN CONFIGURATION
In Capture mode, the CCP1 pin should be configured
as an input by setting the associated TRIS control bit.
Note:
If the CCP1 pin is configured as an output,
a write to the port can cause a capture
condition.
FIGURE 15-1:
CAPTURE MODE
OPERATION BLOCK
DIAGRAM
CCP1
Set Flag bit CCP1IF
Prescaler ^{(PIR1 register)}
 1, 4, 16
CCPR1H
CCPR1L
and
Edge Detect
Capture
Enable
TMR1H
CCP1CON<3:0>
System Clock (FOSC)
TMR1L
15.1.2 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 or when
Timer1 is clocked at FOSC, the capture operation may
not work.
Note:
Clocking Timer1 from the system clock
(FOSC) should not be used in Capture
mode. In order for Capture mode to
recognize the trigger event on the CCP1
pin, Timer1 must be clocked from the
Instruction Clock (FOSC/4) or from an
external clock source.
15.1.3 SOFTWARE INTERRUPT
When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep the
CCP1IE interrupt enable bit of the PIE1 register clear to
avoid false interrupts. Additionally, the user should
clear the CCP1IF interrupt flag bit of the PIR1 register
following any change in operating mode
15.1.4 CCP PRESCALER
There are four prescaler settings specified by the
CCP1M<3:0> bits of the CCP1CON register.
Whenever the CCP module is turned off, or the CCP
module is not in Capture mode, the prescaler counter
is cleared. Any Reset will clear the prescaler counter.
Switching from one capture prescaler to another does not
clear the prescaler and may generate a false interrupt. To
avoid this unexpected operation, turn the module off by
clearing the CCP1CON register before changing the
prescaler (refer to Example 15-1).
EXAMPLE 15-1: CHANGING BETWEEN
CAPTURE PRESCALERS
BANKSEL CCP1CON ;Set Bank bits to point
;to CCP1CON
CLRF CCP1CON ;Turn CCP module off
MOVLW NEW_CAPT_PS ;Load the W reg with
; the new prescaler
; move value and CCP ON
MOVWF CCP1CON ;Load CCP1CON with this
; value
15.1.5 CAPTURE DURING SLEEP
Capture mode depends upon the Timer1 module for
proper operation. There are two options for driving the
Timer1 module in Capture mode. It can be driven by the
instruction clock (FOSC/4), or by an external clock
source.
If Timer1 is clocked by FOSC/4, then Timer1 will not
increment during Sleep. When the device wakes from
Sleep, Timer1 will continue from its previous state.
If Timer1 is clocked by an external clock source, then
Capture mode will operate as defined in Section 15.1
“Capture Mode”.
DS41430B-page 110
Preliminary
 2011 Microchip Technology Inc.