PIC18F258 Datasheet, PDF (125/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

15.2.3 SOFTWARE INTERRUPT
When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep bit
CCP1IE (PIE registers) clear to avoid false interrupts
and should clear the flag bit CCP1IF, following any
such change in Operating mode.
15.2.4 CCP1 PRESCALER
There are four prescaler settings, specified by bits
CCP1M3:CCP1M0. Whenever the CCP1 module is
turned off, or the CCP1 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 15-1 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.
PIC18FXX8
15.2.5 CAN MESSAGE TIME-STAMP
The CAN capture event occurs when a message is
received in either of the receive buffers. The CAN mod-
ule provides a rising edge to the CCP1 module to
cause a capture event. This feature is provided to
time-stamp the received CAN messages.
This feature is enabled by setting the CANCAP bit of
the CAN I/O control register (CIOCON<4>). The mes-
sage receive signal from the CAN module then takes
the place of the events on RC2/CCP1.
EXAMPLE 15-1: CHANGING BETWEEN
CAPTURE PRESCALERS
CLRF CCP1CON, F
MOVLW NEW_CAPT_PS
; Turn CCP module off
; Load WREG with the
; new prescaler mode
; value and CCP ON
MOVWF CCP1CON
; Load CCP1CON with
; this value
FIGURE 15-1:
CAPTURE MODE OPERATION BLOCK DIAGRAM
CCP1 pin
Prescaler
÷ 1, 4, 16
Set Flag bit CCP1IF
(PIR1<2>)
T3CCP1
T3ECCP1
and
Edge Detect
CCP1CON<3:0>
Qs
T3ECCP1
T3CCP1
Note: I/O pins have diode protection to VDD and VSS.
TMR3H TMR3L
TMR3
Enable
CCPR1H CCPR1L
TMR1
Enable
TMR1H
TMR1L
 2002 Microchip Technology Inc.
Preliminary
DS41159B-page 123