PIC18F1220_07 Datasheet, PDF (119/308 Pages) Microchip Technology – 18/20/28-Pin High-Performance, Enhanced Flash Microcontrollers with 10-bit A/D and nanoWatt Technology

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
CLRF CCP1CON
MOVLW NEW_CAPT_PS
MOVWF CCP1CON
; Turn CCP module off
; Load WREG with the
; new prescaler mode
; value and CCP ON
; Load CCP1CON with
; this value
FIGURE 15-1:
CAPTURE MODE OPERATION BLOCK DIAGRAM
CCP1 pin
Prescaler
÷ 1, 4, 16
Set Flag bit CCP1IF
T3CCP1
and
Edge Detect
CCP1CON<3:0>
Q’s
T3CCP1
TMR3H TMR3L
TMR3
Enable
CCPR1H
CCPR1L
TMR1
Enable
TMR1H
TMR1L
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.
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.
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.
© 2007 Microchip Technology Inc.
DS39605F-page 117