PIC16F627A Datasheet, PDF(58/168 Page) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontrollers

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PIC16F627A Datasheet, PDF (58/168 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontrollers

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PIC16F627A/628A/648A

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:

â¢ Every falling edge

â¢ Every rising edge

â¢ Every 4th rising edge

â¢ 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 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.

Note:

If the RB3/CCP1 is configured as an out-

put, a write to the port can cause a capture

condition.

FIGURE 9-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

RB3/CCP1

Set flag bit CCP1IF

Prescaler

(PIR1<2>)

Â³ 1, 4, 16

CCPR1H

and

edge detect

Capture

Enable

CCP1CON<3:0>

Qâs

TMR1H

CCPR1L

TMR1L

9.1.2 TIMER1 MODE SELECTION

Timer1 must be running in Timer mode or synchronized

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 pres-

calers. This example also clears the prescaler counter

and will not generate the âfalseâ interrupt.

EXAMPLE 9-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

CLRF

MOVLW

MOVWF

CCP1CON ;Turn CCP module off

NEW_CAPT_PS ;Load the W reg with

; the new prescaler

; mode value and CCP ON

CCP1CON ;Load CCP1CON with this

; value

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:

â¢ Driven High

â¢ Driven Low

â¢ Remains Unchanged

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

bits CCP1M3:CCP1M0 (CCP1CON<3:0>). At the

same time, interrupt flag bit CCP1IF is set.

FIGURE 9-2:

COMPARE MODE

OPERATION BLOCK

DIAGRAM

Set flag bit CCP1IF

(PIR1<2>)

CCPR1H CCPR1L

RB3/CCP1

TRISB<3>

Output Enable

S Output

R Logic

match

CCP1CON<3:0>

Mode Select

Comparator

TMR1H TMR1L

Note:

Special event trigger will reset Timer1, but not

set interrupt flag bit TMR1IF (PIR1<0>)

DS40044A-page 56

Preliminary

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