PIC16C84A datasheet(49/117 Pages) MICROCHIP

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DS30081F-page 49

PIC16C8X

8.5.1

INT INTERRUPT

External interrupt on RB0/INT pin is edge triggered:

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

falling, if INTEDG bit is clear. When a valid edge

appears

the

RB0/INT

pin,

the

INTF

bit

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

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

must be cleared in software via the interrupt service

routine before re-enabling this interrupt. The INT

interrupt can wake the processor from SLEEP

(Section 8.8) only if the INTE bit was set prior to going

into SLEEP. The status of the GIE bit decides whether

the processor branches to the interrupt vector

following wake-up.

8.5.2

TMR0 INTERRUPT

An overﬂow (FFh

→ 00h) in TMR0 will set ﬂag bit T0IF

(INTCON<2>). The interrupt can be enabled/disabled

by setting/clearing enable bit T0IE (INTCON<5>)

(Section 6.0).

8.5.3

PORT RB INTERRUPT

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<3>)

(Section 5.2).

Note 1: For the PIC16C84 Only;

If a change on an I/O pin should occur

when a read operation of PORTB is being

executed (start of the Q2 cycle), the RBIF

interrupt ﬂag bit may not get set.

Note 2: For all other PIC16C8X devices;

For a change on the I/O pin to be

recognized, the pulse width must be at

least TCY wide.

8.6

Context Saving During Interrupts

During an interrupt, only the return PC value is saved

on the stack. Typically, users wish to save key register

values during an interrupt (e.g., W register and

STATUS register). This is implemented in software.

Example 8-1 stores and restores the STATUS and W

and STATUS_TEMP are the temporary storage

locations for the W and STATUS registers values.

Example 8-1 does the following:

Stores the W register.

Stores the STATUS register in STATUS_TEMP.

Executes the Interrupt Service Routine code.

Restores the STATUS (and bank select bit)

Restores the W register.

EXAMPLE 8-1:

SAVING STATUS AND W REGISTERS IN RAM

PUSH

MOVWF

W_TEMP

; Copy W to TEMP register,

SWAPF

STATUS, W

; Swap status to be saved into W

MOVWF

STATUS_TEMP

; Save status to STATUS_TEMP register

ISR

; Interrupt Service Routine

;

should configure Bank as required

;

POP

SWAPF

STATUS_TEMP, W

; Swap nibbles in STATUS_TEMP register

; and place result into W

MOVWF

STATUS

; Move W into STATUS register

;

(sets bank to original state)

SWAPF

W_TEMP, F

; Swap nibbles in W_TEMP and place result in W_TEMP

SWAPF

W_TEMP, W

; Swap nibbles in W_TEMP and place result into W

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