PIC16F87 datasheet(82/230 Pages) MICROCHIP

82 / 230 page

PIC16F87/88

DS30487D-page 82

 2002-2013 Microchip Technology Inc.

9.1

Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

16-bit value of the TMR1 register when an event occurs

on the CCP1 pin. 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 is overwritten by the new captured value.

9.1.1

CCP PIN CONFIGURATION

In Capture mode, the CCP1 pin should be configured

as an input by setting the TRISB<x> bit.

FIGURE 9-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

9.1.2

TIMER1 MODE SELECTION

Timer1 must be running in Timer mode or Synchro-

nized Counter mode for the CCP module to use the

capture feature. In Asynchronous Counter mode, the

capture operation may not work.

9.1.3

SOFTWARE INTERRUPT

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.

9.1.4

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 9-1 shows the recom-

mended

method

for

switching

between

capture

prescalers. This example also clears the prescaler

counter and will not generate the “false” interrupt.

EXAMPLE 9-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note 1: If the CCP1 pin is configured as an

output, a write to the port can cause a

capture condition.

2: The TRISB bit (0 or 3) is dependent upon

the

setting

configuration

bit

(CCPMX).

CCPR1H

CCPR1L

TMR1H

TMR1L

Set Flag bit CCP1IF

(PIR1<2>)

Capture

Enable

CCP1CON<3:0>

CCP1 pin

Prescaler

 1, 4, 16

and

Edge Detect

CLRF

CCP1CON

;Turn CCP module off

MOVLW

NEW_CAPT_PS ;Load the W reg with

;the new prescaler

;move value and CCP ON

MOVWF

CCP1CON

;Load CCP1CON with this

;value

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