PIC18F-LF1XK50 Datasheet, PDF (119/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

PIC18F/LF1XK50
14.2 Capture Mode
In Capture mode, the CCPR1H:CCPR1L register pair
captures the 16-bit value of the TMR1 or TMR3
registers when an event occurs on the corresponding
CCP1 pin. 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 the mode select bits,
CCP1M<3:0> of the CCP1CON register. When a cap-
ture is made, the interrupt request flag bit, CCP1IF, is
set; it must be cleared by software. If another capture
occurs before the value in register CCPR1 is read, the
old captured value is overwritten by the new captured
value.
14.2.1 CCP PIN CONFIGURATION
In Capture mode, the appropriate CCP1 pin should be
configured as an input by setting the corresponding
TRIS direction bit.
Note:
If the CCP1 pin is configured as an output,
a write to the port can cause a capture
condition.
14.2.2 TIMER1/TIMER3 MODE SELECTION
The timers that are to be used with the capture feature
(Timer1 and/or Timer3) must be running in Timer mode or
Synchronized Counter mode. In Asynchronous Counter
mode, the capture operation may not work. The timer to
be used with each CCP module is selected in the T3CON
register (see Section 14.1.1 “CCP Module and Timer
Resources”).
14.2.3 SOFTWARE INTERRUPT
When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep the
CCP1IE interrupt enable bit clear to avoid false inter-
rupts. The interrupt flag bit, CCP1IF, should also be
cleared following any such change in operating mode.
14.2.4 CCP PRESCALER
There are four prescaler settings in Capture mode; they
are specified as part of the operating mode selected by
the mode select bits (CCP1M<3:0>). Whenever the
CCP module is turned off or Capture mode is disabled,
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 14-1 shows the
recommended method for switching between capture
prescalers. This example also clears the prescaler
counter and will not generate the “false” interrupt.
EXAMPLE 14-1: CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF
MOVLW
MOVWF
CCP1CON
; Turn CCP module off
NEW_CAPT_PS ; Load WREG with the
; new prescaler mode
; value and CCP ON
CCP1CON
; Load CCP1CON with
; this value
FIGURE 14-1:
CAPTURE MODE OPERATION BLOCK DIAGRAM
CCP1 pin
Set CCP1IF
T3CCP1
Prescaler
 1, 4, 16
and
Edge Detect
T3CCP1
CCP1CON<3:0> ⁴
Q1:Q4 ⁴
TMR3H
TMR3L
TMR3
Enable
CCPR1H CCPR1L
TMR1
Enable
TMR1H
TMR1L
 2010 Microchip Technology Inc.
Preliminary
DS41350E-page 119