PIC16LC712 datasheet(62/106 Pages) MICROCHIP

62 / 106 page

PIC16C712/716

DS41106C-page 62

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9.10.1

INT INTERRUPT

External interrupt on RB0/INT pin is edge triggered,

either rising if bit INTEDG (OPTION_REG<6>) is set,

or falling if the INTEDG bit is clear. When a valid edge

appears

the

RB0/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

Routine before re-enabling this interrupt. The INT inter-

rupt can wake-up the processor from Sleep, if bit INTE

was set prior to going into Sleep. The status of global

interrupt enable bit GIE decides whether or not the

processor branches to the interrupt vector following

wake-up. See Section 9.13 “Power-down Mode

(Sleep)” for details on Sleep mode.

9.10.2

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 4.0 “Timer0 Module”)

9.10.3

PORTB INTCON CHANGE

An input change on PORTB<7:4> sets flag bit RBIF

(INTCON<0>). The interrupt can be enabled/disabled

by setting/clearing enable bit RBIE (INTCON<4>).

(Section 3.2 “PORTB and the TRISB Register”)

9.11

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

Example 9-1 stores and restores the W and STATUS

registers. The register, W_TEMP, must be defined in

each bank 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).

The example:

Stores the W register.

Stores the STATUS register in bank 0.

Stores the PCLATH register.

Executes the Interrupt Service Routine code

(User-generated).

Restores the STATUS register (and bank select

bit).

Restores the W and PCLATH registers.

EXAMPLE 9-1:

SAVING STATUS, W, AND PCLATH 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

CLRF

STATUS

;bank 0, regardless of current bank, Clears IRP,RP1,RP0

MOVWF

STATUS_TEMP

;Save status to bank zero STATUS_TEMP register

MOVF

PCLATH, W

;Only required if using pages 1, 2 and/or 3

MOVWF

PCLATH_TEMP

;Save PCLATH into W

CLRF

PCLATH

;Page zero, regardless of current page

BCF

STATUS, IRP

;Return to Bank 0

MOVF

FSR, W

;Copy FSR to W

MOVWF

FSR_TEMP

;Copy FSR from W to FSR_TEMP

:(ISR)

MOVF

PCLATH_TEMP, W

;Restore PCLATH

MOVWF

PCLATH

;Move W into PCLATH

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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