PIC16F-ESLASHSS datasheet(58/178 Pages) MICROCHIP

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PIC16F627A/628A/648A

DS40044F-page 56

9.1

Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

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

on pin RB3/CCP1. 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 CCP1M<3:0>

(CCP1CON<3:0>). When a capture is made, the

interrupt 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 will be lost.

9.1.1

CCP PIN CONFIGURATION

In Capture mode, the RB3/CCP1 pin should be config-

ured as an input by setting the TRISB<3> 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

CCP1M<3:0>. 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

recommended 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

9.2

Compare Mode

In Compare mode, the 16-bit CCPR1 register value is

constantly compared against the TMR1 register pair

value. When a match occurs, the RB3/CCP1 pin is:

• Driven high

•Driven low

• Remains unchanged

The action on the pin is based on the value of control

bits CCP1M<3:0> (CCP1CON<3:0>). At the same

time, interrupt flag bit CCP1IF is set.

FIGURE 9-2:

COMPARE MODE

OPERATION BLOCK

DIAGRAM

Note:

If the RB3/CCP1 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

Q’s

CCP1CON<3:0>

RB3/CCP1

Prescaler

³ 1, 4, 16

and

edge detect

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

CCPR1H CCPR1L

TMR1H

TMR1L

Comparator

Output

Logic

Set flag bit CCP1IF

(PIR1<2>)

match

RB3/CCP1

TRISB<3>

CCP1CON<3:0>

Mode Select

Output Enable

Note:

Special event trigger will reset Timer1, but not

set interrupt flag bit TMR1IF (PIR1<0>).

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