PIC16F684-ESLASHST datasheet(78/164 Pages) MICROCHIP

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PIC16F684

DS41202C-page 76

Preliminary

 2004 Microchip Technology Inc.

11.1

Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

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

on pin RC5/CCP1/P1A. An event is defined as one of

the following and is configured by CCP1CON<3:0>:

• Every falling edge

• Every rising edge

• Every 4th rising edge

• Every 16th rising edge

When a capture is made, the interrupt request flag bit,

CCP1IF (PIR1<5>), is set. The interrupt flag 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.

11.1.1

CCP1 PIN CONFIGURATION

In Capture mode, the RC5/CCP1/P1A pin should be

configured as an input by setting the TRISC<5> bit.

FIGURE 11-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

11.1.2

TIMER1 MODE SELECTION

Timer1 must be running in Timer mode or Synchro-

nized Counter mode for the ECCP module to use the

capture feature. In Asynchronous Counter mode, the

capture operation may not work.

11.1.3

SOFTWARE INTERRUPT

When the Capture mode is changed, a false capture

interrupt may be generated. The user should keep bit

CCP1IE (PIE1<5>) clear to avoid false interrupts and

should clear the flag bit CCP1IF (PIR1<5>) following

any such change in operating mode.

11.1.4

ECCP PRESCALER

There are four prescaler settings specified by bits

CCP1M<3:0> (CCP1CON<3:0>). Whenever the ECCP

module is turned off, or the ECCP module is not in

Capture mode, the prescaler counter is cleared. 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 11-1 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 11-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note:

If the RC5/CCP1/P1A pin is configured as

an output, a write to the port can cause a

capture condition.

CCPR1H

CCPR1L

TMR1H

TMR1L

Set Flag bit CCP1IF

(PIR1<5>)

Capture

Enable

Q’s

CCP1CON<3:0>

RC5/CCP1/P1A

Prescaler

÷ 1, 4, 16

and

Edge Detect

CLRF

CCP1CON

;Turn ECCP module off

MOVLW

NEW_CAPT_PS ;Load the W reg with

;the new prescaler

;move value and ECCP ON

MOVWF

CCP1CON

;Load CCP1CON with this

;value

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