PIC16F7X Datasheet, PDF(57/174 Page) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

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PIC16F7X Datasheet, PDF (57/174 Pages) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

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8.3 Capture Mode

In Capture mode, CCPR1H:CCPR1L captures the

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

on pin RC2/CCP1. An event is defined as one of the fol-

lowing and is configured by CCPxCON<3:0>:

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. 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.

8.3.1 CCP PIN CONFIGURATION

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

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

Note:

If the RC2/CCP1 pin is configured as an

output, a write to the port can cause a

capture condition.

FIGURE 8-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

Set Flag bit CCP1IF

Prescaler

(PIR1<2>)

Ã· 1, 4, 16

RC2/CCP1

CCPR1H

and

Edge Detect

Capture

Enable

CCP1CON<3:0>

Qâs

TMR1H

CCPR1L

TMR1L

8.3.2 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.

8.3.3 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.

PIC16F7X

8.3.4 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. 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 âfalseâ interrupt.

EXAMPLE 8-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

CLRF

MOVLW

MOVWF

CCP1CON ;Turn CCP module off

NEW_CAPT_PS ;Load the W reg with

;the new prescaler

;move value and CCP ON

CCP1CON ;Load CCP1CON with this

;value

8.4 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 RC2/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 8-2:

COMPARE MODE

OPERATION BLOCK

DIAGRAM

CCP1CON<3:0>

Mode Select

Set Flag bit CCP1IF

(PIR1<2>)

CCPR1H CCPR1L

RC2/CCP1

Q S Output

R Logic

TRISC<2>

Output Enable

Comparator

Match

TMR1H TMR1L

Special Event Trigger

Special Event Trigger will:

â¢ clear TMR1H and TMR1L registers

â¢ NOT set interrupt flag bit TMR1F (PIR1<0>)

â¢ (for CCP2 only) set the GO/DONE bit (ADCON0<2>)

DS30325B-page 55

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