PIC12F1822-ISLASHMF datasheet(200/398 Pages) MICROCHIP

200 / 398 page

PIC12F/LF1822/16F/LF1823

DS41413A-page 200

Preliminary

 2010 Microchip Technology Inc.

23.1

Capture Mode

Capture mode makes use of the 16-bit Timer1

resource. When an event occurs on the CCP1 pin, the

16-bit CCPR1H:CCPR1L register pair captures and

stores the 16-bit value of the TMR1H:TMR1L register

pair, respectively. An event is defined as one of the

following and is configured by the CCP1M<3:0> bits of

the CCP1CON register:

• Every falling edge

• Every rising edge

• Every 4th rising edge

• Every 16th rising edge

When a capture is made, the Interrupt Request Flag bit

CCP1IF of the PIR1 register is set. The interrupt flag

must be cleared in software. If another capture occurs

before the value in the CCPR1H, CCPR1L register pair

is read, the old captured value is overwritten by the new

captured value.

Figure 23-1 shows a simplified diagram of the Capture

operation.

23.1.1

CCP1 PIN CONFIGURATION

In Capture mode, the CCP1 pin should be configured

as an input by setting the associated TRIS control bit.

Also, the CCP1 pin function may be moved to

alternative pins using the APFCON register. Refer to

Section 12.1 “Alternate Pin Function” for more

details.

FIGURE 23-1:

CAPTURE MODE

OPERATION BLOCK

DIAGRAM

23.1.2

TIMER1 MODE RESOURCE

Timer1 must be running in Timer mode or Synchronized

Counter mode for the CCP1 module to use the capture

feature. In Asynchronous Counter mode, the capture

operation may not work.

See Section 20.0 “Timer1 Module with Gate Control”

for more information on configuring Timer1.

23.1.3

SOFTWARE INTERRUPT MODE

When the Capture mode is changed, a false capture

interrupt may be generated. The user should keep the

CCP1IE interrupt enable bit of the PIE1 register clear to

avoid false interrupts. Additionally, the user should

clear the CCP1IF interrupt flag bit of the PIR1 register

following any change in Operating mode.

23.1.4

CCP1 PRESCALER

There are four prescaler settings specified by the

CCP1M<3:0>

bits

the

CCP1CON

Whenever the CCP1 module is turned off, or the CCP1

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 does not

clear the prescaler and may generate a false interrupt. To

avoid this unexpected operation, turn the module off by

clearing the CCP1CON register before changing the

prescaler. Example 23-1 demonstrates the code to

perform this function.

EXAMPLE 23-1:

CHANGING BETWEEN

CAPTURE PRESCALERS

Note:

If the CCP1 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 register)

Capture

Enable

CCP1M<3:0>

Prescaler

 1, 4, 16

and

Edge Detect

CCP1

System Clock (FOSC)

Note:

Clocking Timer1 from the system clock

(FOSC) should not be used in Capture

mode. In order for Capture mode to

recognize the trigger event on the CCP1

pin, Timer1 must be clocked from the

instruction clock (FOSC/4) or from an

external clock source.

BANKSEL CCP1CON

;Set Bank bits to point

;to CCP1CON

CLRF

CCP1CON

;Turn CCP1 module off

MOVLW

NEW_CAPT_PS ;Load the W reg with

;the new prescaler

;move value and CCP1 ON

MOVWF

CCP1CON

;Load CCP1CON with this

;value

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