Datasheet

Table Of Contents
© 2007 Microchip Technology Inc. DS39605F-page 117
PIC18F1220/1320
15.3.4 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 15-1 shows the
recommended method for switching between capture
prescalers. This example also clears the prescaler
counter and will not generate the “false” interrupt.
EXAMPLE 15-1: CHANGING BETWEEN
CAPTURE PRESCALERS
FIGURE 15-1: CAPTURE MODE OPERATION BLOCK DIAGRAM
15.4 Compare Mode
In Compare mode, the 16-bit CCPR1 register value is
constantly compared against either the TMR1 register
pair value, or the TMR3 register pair value. When a
match occurs, the RB3/CCP1/P1A pin:
Is driven high
•Is driven low
Toggles output (high-to-low or low-to-high)
Remains unchanged (interrupt only)
The action on the pin is based on the value of control
bits, CCP1M3:CCP1M0. At the same time, interrupt
flag bit, CCP1IF, is set.
15.4.1 CCP PIN CONFIGURATION
The user must configure the RB3/CCP1/P1A pin as an
output by clearing the TRISB<3> bit.
15.4.2 TIMER1/TIMER3 MODE SELECTION
Timer1 and/or Timer3 must be running in Timer mode
or Synchronized Counter mode if the CCP module is
using the compare feature. In Asynchronous Counter
mode, the compare operation may not work.
15.4.3 SOFTWARE INTERRUPT MODE
When generate software interrupt is chosen, the RB3/
CCP1/P1A pin is not affected. CCP1IF is set and an
interrupt is generated (if enabled).
15.4.4 SPECIAL EVENT TRIGGER
In this mode, an internal hardware trigger is generated,
which may be used to initiate an action.
The special event trigger output of CCP1 resets the
TMR1 register pair. This allows the CCPR1 register to
effectively be a 16-bit programmable period register for
Timer1.
The special event trigger also sets the GO/DONE
bit
(ADCON0<1>). This starts a conversion of the
currently selected A/D channel if the A/D is on.
CLRF CCP1CON ; Turn CCP module off
MOVLW NEW_CAPT_PS ; Load WREG with the
; new prescaler mode
; value and CCP ON
MOVWF CCP1CON ; Load CCP1CON with
; this value
CCPR1H CCPR1L
TMR1H TMR1L
Set Flag bit CCP1IF
TMR3
Enable
Q’s
CCP1CON<3:0>
CCP1 pin
Prescaler
÷ 1, 4, 16
and
Edge Detect
TMR3H TMR3L
TMR1
Enable
T3CCP1
T3CCP
1
Note: Clearing the CCP1CON register will force
the RB3/CCP1/P1A compare output latch
to the default low level. This is not the
PORTB I/O data latch.