PIC16F74-ESLASHSS datasheet(102/174 Pages) MICROCHIP

102 / 174 page

PIC16F7X

DS30325B-page 100

 2002 Microchip Technology Inc.

12.11.1

INT INTERRUPT

External interrupt on the 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 pro-

cessor branches to the interrupt vector following wake-

up. See Section 12.14 for details on SLEEP mode.

12.11.2

TMR0 INTERRUPT

An overflow (FFh

→ 00h) in the TMR0 register will set

flag bit TMR0IF (INTCON<2>). The interrupt can be

enabled/disabled

setting/clearing

enable

bit

TMR0IE (INTCON<5>). (Section 5.0)

12.11.3

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>), see

Section 4.2.

12.12 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, PCLATH and STA-

TUS registers). This will have to be implemented in

software, as shown in Example 12-1.

For the PIC16F73/74 devices, the register W_TEMP

must be defined in both banks 0 and 1 and must be

defined at the same offset from the bank base address

(i.e., If W_TEMP is defined at 20h in bank 0, it must

also be defined at A0h in bank 1.). The registers,

PCLATH_TEMP and STATUS_TEMP, are only defined

in bank 0.

Since the upper 16 bytes of each bank are common in

the PIC16F76/77 devices, temporary holding registers

W_TEMP,

STATUS_TEMP

and

PCLATH_TEMP

should be placed in here. These 16 locations don’t

require banking and, therefore, make it easier for con-

text save and restore. The same code shown in

Example 12-1 can be used.

EXAMPLE 12-1:

SAVING STATUS, W, AND PCLATH REGISTERS IN RAM

MOVWF

W_TEMP

;Copy W to TEMP register

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

:(ISR)

;Insert user code here

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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