PIC16C925-SSLASHCL datasheet(56/182 Pages) MICROCHIP

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PIC16C925/926

DS39544A-page 54

Preliminary

 2001 Microchip Technology Inc.

8.1

Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

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

on pin RC2/CCP1 (Figure 8-1). An event can be

selected to be one of the following:

• 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 with the new captured value.

8.1.1

CCP PIN CONFIGURATION

In Capture mode, the RC2/CCP1 pin should be config-

ured as an input by setting the TRISC<2> bit.

FIGURE 8-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

8.1.2

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.

8.1.3

SOFTWARE INTERRUPT

When the Capture mode is changed, a false capture

interrupt may be generated. The user should keep

enable bit CCP1IE (PIE1<2>) clear to avoid false inter-

rupts and should clear flag bit CCP1IF following any

such change in operating mode.

8.1.4

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 8-1 shows the recom-

mended method for switching between capture pres-

calers. This example also clears the prescaler counter

and will not generate the “false” interrupt.

EXAMPLE 8-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note:

If the RC2/CCP1 pin is configured as an

output, a write to the port can cause a cap-

ture condition.

CCPR1H

CCPR1L

TMR1H

TMR1L

Set CCP1IF

PIR1<2>

Capture

Enable

Q’s

CCP1CON<3:0>

RC2/CCP1

Prescaler

÷ 1, 4, 16

and

edge detect

CCP

CLRF

CCP1CON

; Turn CCP module off

MOVLW

NEW_CAPT_PS ; Load the W reg with

; the new prescaler

; mode value and CCP ON

MOVWF

CCP1CON

; Load CCP1CON with

; this value

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