PIC16F84A datasheet(33/90 Pages) MICROCHIP

33 / 90 page

 2001-2013 Microchip Technology Inc.

DS35007C-page 33

PIC16F84A

6.11.3

WAKE-UP USING INTERRUPTS

When global interrupts are disabled (GIE cleared) and

any interrupt source has both its interrupt enable bit

and interrupt flag bit set, one of the following will occur:

• If the interrupt occurs before the execution of a

SLEEP

instruction, the SLEEP instruction will com-

plete as a NOP. Therefore, the WDT and WDT

postscaler will not be cleared, the TO bit will not

be set and PD bits will not be cleared.

• If the interrupt occurs during or after the execu-

tion of a SLEEP instruction, the device will imme-

diately wake-up from SLEEP. The SLEEP

instruction will be completely executed before the

wake-up. Therefore, the WDT and WDT

postscaler will be cleared, the TO bit will be set

and the PD bit will be cleared.

Even if the flag bits were checked before executing a

SLEEP

instruction, it may be possible for flag bits to

become set before the SLEEP instruction completes. To

determine whether a SLEEP instruction executed, test

the PD bit. If the PD bit is set, the SLEEP instruction

was executed as a NOP.

To ensure that the WDT is cleared, a CLRWDT instruc-

tion should be executed before a SLEEP instruction.

6.12

Program Verification/Code

Protection

If the code protection bit(s) have not been pro-

grammed, the on-chip program memory can be read

out for verification purposes.

6.13

ID Locations

Four memory locations (2000h - 2004h) are designated

as ID locations to store checksum or other code

identification

numbers.

These

locations

are

not

accessible during normal execution but are readable

and writable only during program/verify. Only the

four Least Significant bits of ID location are usable.

6.14

In-Circuit Serial Programming

PIC16F84A

microcontrollers

can

serially

programmed while in the end application circuit. This is

simply done with two lines for clock and data, and three

other lines for power, ground, and the programming

voltage. Customers can manufacture boards with

unprogrammed

devices,

and

then

program

the

microcontroller just before shipping the product,

allowing the most recent firmware or custom firmware

to be programmed.

For complete details of Serial Programming, please

refer to the In-Circuit Serial Programming™ (ICSP™)

Guide, (DS30277).

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