PIC12CE673-04SLASHP datasheet(56/116 Pages) MICROCHIP

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PIC12CE67X

DS40181B-page 56

Preliminary

9.5.1

TMR0 INTERRUPT

An overﬂow (FFh

→ 00h) in the TMR0 register will set

ﬂag bit T0IF (INTCON<2>). The interrupt can be

enabled/disabled by setting/clearing enable bit T0IE

(INTCON<5>). (Section 7.0)

9.5.2

INT INTERRUPT

External interrupt on GP2/INT pin is edge triggered:

either rising if bit INTEDG (OPTION<6>) is set, or fall-

ing, if the INTEDG bit is clear. When a valid edge

appears

the

GP2/INT

pin,

ﬂag

bit

INTF

(INTCON<1>) is set. This interrupt can be disabled by

clearing enable bit INTE (INTCON<4>). Flag bit INTF

must be cleared in software in the interrupt service rou-

tine before re-enabling this interrupt. The INT interrupt

can wake-up the processor from SLEEP, if bit INTE was

set prior to going into SLEEP. The status of global inter-

rupt enable bit GIE decides whether or not the proces-

sor branches to the interrupt vector following wake-up.

See Section 9.8 for details on SLEEP mode.

9.5.3

GPIO INTCON CHANGE

An input change on GP3, GP1 or GP0 sets ﬂag bit

GPIF (INTCON<0>). The interrupt can be enabled/dis-

abled

setting/clearing

enable

bit

GPIE

(INTCON<3>). (Section 5.1)

9.6

Context Saving During Interrupts

During an interrupt, only the return PC value is saved

on the stack. Typically, users may wish to save key reg-

isters during an interrupt i.e., W register and STATUS

The example:

Stores the W register.

Stores the STATUS register in bank 0.

Executes the ISR code.

Restores the STATUS register (and bank select

bit).

Restores the W register.

Example 9-1 store and restore the STATUS and W

registers. The register, W_TEMP, must be deﬁned in

both banks and must be deﬁned at the same offset

from the bank base address (i.e., if W_TEMP is

deﬁned at 0x20 in bank 0, it must also be deﬁned at

0xA0 in bank 1).

EXAMPLE 9-1:

SAVING STATUS AND W REGISTERS IN RAM

MOVWF

W_TEMP

;Copy W to TEMP register, could be bank one or zero

SWAPF

STATUS,W

;Swap status to be saved into W

BCF

STATUS,RP0

;Change to bank zero, regardless of current bank

MOVWF

STATUS_TEMP

;Save status to bank zero STATUS_TEMP register

:(ISR)

SWAPF

STATUS_TEMP,W

;Swap STATUS_TEMP register into W

;(sets bank to original state)

MOVWF

STATUS

;Move W into STATUS register

SWAPF

W_TEMP,F

;Swap W_TEMP

SWAPF

W_TEMP,W

;Swap W_TEMP into W

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