PIC16F877ATISLASHML datasheet(140/234 Pages) MICROCHIP

140 / 234 page

PIC16F87XA

DS39582B-page 138

 2003 Microchip Technology Inc.

FIGURE 12-3:

COMPARATOR OUTPUT BLOCK DIAGRAM

12.6

Comparator Interrupts

The comparator interrupt flag is set whenever there is

a change in the output value of either comparator.

Software will need to maintain information about the

status of the output bits, as read from CMCON<7:6>, to

determine the actual change that occurred. The CMIF

bit (PIR registers) is the Comparator Interrupt Flag. The

CMIF bit must be reset by clearing it (‘0’). Since it is

also possible to write a ‘1’ to this register, a simulated

interrupt may be initiated.

The CMIE bit (PIE registers) and the PEIE bit (INTCON

the GIE bit must also be set. If any of these bits are

clear, the interrupt is not enabled, though the CMIF bit

will still be set if an interrupt condition occurs.

The user, in the Interrupt Service Routine, can clear the

interrupt in the following manner:

Any read or write of CMCON will end the

mismatch condition.

Clear flag bit CMIF.

A mismatch condition will continue to set flag bit CMIF.

Reading CMCON will end the mismatch condition and

allow flag bit CMIF to be cleared.

To RA4 or

RA5 Pin

Bus

Data

Read CMCON

Set

MULTIPLEX

CMIF

bit

Port Pins

Read CMCON

Reset

From

Other

Comparator

CxINV

Note:

If a change in the CMCON register

(C1OUT or C2OUT) should occur when a

read operation is being executed (start of

the Q2 cycle), then the CMIF (PIR

registers) interrupt flag may not get set.

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