PIC12F635ESS datasheet(52/234 Pages) MICROCHIP

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PIC12F635/PIC16F636/639

DS41232D-page 50

4.2.2

INTERRUPT-ON-CHANGE

Each of the PORTA pins is individually configurable as

an interrupt-on-change pin. Control bits, IOCAx, enable

or disable the interrupt function for each pin. Refer to

Power-on Reset.

For enabled interrupt-on-change pins, the values are

compared with the old value latched on the last read of

PORTA. The ‘mismatch’ outputs of the last read are

OR’d together to set the PORTA Change Interrupt Flag

bit (RAIF) in the INTCON register.

This interrupt can wake the device from Sleep. The

user, in the Interrupt Service Routine, clears the

interrupt by:

Any read or write of PORTA. This will end the

mismatch condition, then

Clear the flag bit RAIF.

A mismatch condition will continue to set flag bit RAIF.

Reading PORTA will end the mismatch condition and

allow flag bit RAIF to be cleared. The latch holding the

last read value is not affected by a MCLR nor BOR

Reset. After these Resets, the RAIF flag will continue

to be set if a mismatch is present.

Note:

If a change on the I/O pin should occur

when the read operation is being executed

(start of the Q2 cycle), then the RAIF

interrupt flag may not get set.

IOCA: INTERRUPT-ON-CHANGE PORTA REGISTER

U-0

R/W-0

—

—IOCA5(2)

IOCA4(2)

IOCA3(3)

IOCA2

IOCA1

IOCA0

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7-6

Unimplemented: Read as ‘0’

bit 5-0

IOCA<5:0>: Interrupt-on-Change PORTA Control bits(2,3)

= Interrupt-on-change enabled(1)

= Interrupt-on-change disabled

Note 1: Global Interrupt Enable (GIE) must be enabled for individual interrupts to be recognized.

2: IOCA<5:4> always reads ‘0’ in XT, HS and LP Oscillator modes.

3: IOCA<3> is ignored when WUR is enabled and the device is in Sleep mode.

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