PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 111

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

13.3
In Capture mode, CCPR1H:CCPR1L captures the 16-
bit value of the TMR1 or TMR3 registers 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 will be lost.
13.3.1
In Capture mode, the RC2/CCP1 pin should be config-
ured as an input by setting the TRISC<2> bit.
13.3.2
The timers that are to be used with the capture feature
(either 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.
FIGURE 13-1: CAPTURE MODE OPERATION BLOCK DIAGRAM
Note:
7/99 Microchip Technology Inc.
Capture Mode
CCP PIN CONFIGURATION
TIMER1/TIMER3 MODE SELECTION
If the RC2/CCP1 is configured as an out-
put, a write to the port can cause a capture
condition.
CCP1 Pin
CCP2 Pin
edge detect
edge detect
Q’s
Q’s
Prescaler
Prescaler
1, 4, 16
1, 4, 16
and
and
CCP1CON<3:0>
CCP2CON<3:0>
Set flag bit CCP1IF
Set flag bit CCP2IF
T3CCP1
T3CCP2
T3CCP2
T3CCP1
Preliminary
T3CCP2
T3CCP2
13.3.3
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.
13.3.4
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 13-1 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 13-1: CHANGING BETWEEN
CLRF
MOVLW
MOVWF
SOFTWARE INTERRUPT
CCP PRESCALER
NEW_CAPT_PS
CCP1CON
CCP1CON, F
TMR1
Enable
TMR1
Enable
TMR3
Enable
TMR3
Enable
CAPTURE PRESCALERS
TMR3H
CCPR1H
TMR1H
TMR3H
CCPR2H
TMR1H
PIC18CXX2
; Turn CCP module off
; Load WREG with the
; new prescaler mode
; value and CCP ON
; Load CCP1CON with
; this value
TMR3L
CCPR1L
TMR1L
TMR3L
CCPR2L
TMR1L
DS39026B-page 111