PIC16F631/677/685/687/689/690
11.1.2
TIMER1 MODE SELECTION
11.1 Capture Mode
Timer1 must be running in Timer mode or Synchronized
Counter mode for the CCP module to use the capture
feature. In Asynchronous Counter mode, the capture
operation may not work.
In Capture mode, CCPR1H:CCPR1L captures the
16-bit value of the TMR1 register when an event occurs
on pin CCP1. An event is defined as one of the
following and is configured by the CCP1M<3:0> bits of
the CCP1CON register:
11.1.3
SOFTWARE INTERRUPT
• Every falling edge
• Every rising edge
When the Capture mode is changed, a false capture
interrupt may be generated. The user should keep the
CCP1IE interrupt enable bit of the PIE1 register clear to
avoid false interrupts. Additionally, the user should
clear the CCP1IF interrupt flag bit of the PIR1 register
following any change in operating mode.
• Every 4th rising edge
• Every 16th rising edge
When a capture is made, the Interrupt Request Flag bit
CCP1IF of the PIR1 register is set. The interrupt flag
must be cleared in software. If another capture occurs
before the value in the CCPR1H, CCPR1L register pair
is read, the old captured value is overwritten by the new
captured value (see Figure 11-1).
11.1.4
CCP PRESCALER
There are four prescaler settings specified by the
CCP1M<3:0> bits of the CCP1CON register.
Whenever the CCP module is turned off, or the CCP
module is not in Capture mode, the prescaler counter
is cleared. Any Reset will clear the prescaler counter.
11.1.1
CCP1 PIN CONFIGURATION
In Capture mode, the CCP1 pin should be configured
as an input by setting the associated TRIS control bit.
Switching from one capture prescaler to another does not
clear the prescaler and may generate a false interrupt. To
avoid this unexpected operation, turn the module off by
clearing the CCP1CON register before changing the
prescaler (see Example 11-1).
Note:
If the CCP1 pin is configured as an output,
a write to the port can cause a capture
condition.
FIGURE 11-1:
CAPTURE MODE
OPERATION BLOCK
DIAGRAM
EXAMPLE 11-1:
CHANGING BETWEEN
CAPTURE PRESCALERS
BANKSELCCP1CON
;Set Bank bits to point
;to CCP1CON
;Turn CCP module off
Set Flag bit CCP1IF
(PIR1 register)
Prescaler
÷ 1, 4, 16
CLRF
CCP1CON
MOVLW
NEW_CAPT_PS;Load the W reg with
; the new prescaler
CCP1
pin
CCPR1H
CCPR1L
; move value and CCP ON
Capture
Enable
MOVWF
CCP1CON
;Load CCP1CON with this
; value
and
Edge Detect
TMR1H
TMR1L
CCP1CON<3:0>
System Clock (FOSC)
DS41262D-page 128
© 2007 Microchip Technology Inc.
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