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Sheet目录3753

94页 95页 96页 97页 [98页]99页 100页 101页 102页

2005 Microchip Technology Inc.

Preliminary

DS41265A-page 185

PIC16F946

15.1

Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

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

on pin RC5/T1CKI/CCP1/SEG10. An event is defined

as one of the following:

Every falling edge

Every rising edge

Every 4th rising edge

Every 16th rising edge

The type of event is configured by control bits

CCP1M<3:0> (CCPxCON<3:0>). When a capture is

made, the interrupt request flag bit CCP1IF (PIR1<2>)

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 value.

15.1.1

CCP PIN CONFIGURATION

In Capture mode, the RC5/T1CKI/CCP1/SEG10 pin

should be configured as an input by setting the

TRISC<5> bit.

FIGURE 15-3:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

15.1.2

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.

15.1.3

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.

15.1.4

CCP PRESCALER

There are four prescaler settings, specified by bits

CCP1M<3:0>. 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.

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 recom-

mended method for switching between capture pre-

scalers. This example also clears the prescaler counter

and will not generate the “false” interrupt.

EXAMPLE 15-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note:

If the RC5/T1CKI/CCP1/SEG10 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<2>)

Capture

Enable

CCP1CON<3:0>

RC5/T1CKI/

Prescaler

÷ 1, 4, 16

and

edge detect

CCP1/SEG10

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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