PIC16F84A datasheet(21/68 Pages) MICROCHIP

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PIC16F84A

Preliminary

DS35007A-page 21

6.0

SPECIAL FEATURES OF THE

CPU

What

sets

microcontroller

apart

from

other

processors are special circuits to deal with the needs of

real time applications. The PIC16F84A has a host of

such features intended to maximize system reliability,

minimize

cost

through

elimination

external

components, provide power saving operating modes

and offer code protection. These features are:

• OSC Selection

• Reset

- Power-on Reset (POR)

- Power-up Timer (PWRT)

- Oscillator Start-up Timer (OST)

• Interrupts

• Watchdog Timer (WDT)

• SLEEP

• Code protection

• ID locations

• In-circuit serial programming

The PIC16F84A has a Watchdog Timer which can be

shut off only through conﬁguration bits. It runs off its

own RC oscillator for added reliability. There are two

timers that offer necessary delays on power-up. One is

the Oscillator Start-up Timer (OST), intended to keep

the chip in reset until the crystal oscillator is stable. The

other is the Power-up Timer (PWRT), which provides a

ﬁxed delay of 72 ms (nominal) on power-up only. This

design keeps the device in reset while the power supply

stabilizes. With these two timers on-chip, most

applications need no external reset circuitry.

SLEEP mode offers a very low current power-down

mode. The user can wake-up from SLEEP through

external reset, Watchdog Timer time-out or through an

interrupt. Several oscillator options are provided to

allow the part to ﬁt the application. The RC oscillator

option saves system cost while the LP crystal option

saves power. A set of conﬁguration bits are used to

select the various options.

Additional information on special features is available in

the

PICmicro™

Mid-Range

Reference

Manual,

(DS33023).

6.1

Conﬁguration Bits

The conﬁguration bits can be programmed (read as '0')

or left unprogrammed (read as '1') to select various

device conﬁgurations. These bits are mapped in

program memory location 2007h.

Address 2007h is beyond the user program memory

space and it belongs to the special test/conﬁguration

memory space (2000h - 3FFFh). This space can only

be accessed during programming.

FIGURE 6-1:

CONFIGURATION WORD - PIC16F84A

R/P-u

R/P-u R/P-u R/P-u R/P-u R/P-u

R/P-u

PWRTE WDTE FOSC1 FOSC0

bit13

bit0

= Readable bit

= Programmable bit

- n = Value at POR reset

u = unchanged

bit 13:4 CP: Code Protection bit

1 = Code protection off

0 = All memory is code protected

bit 3

PWRTE: Power-up Timer Enable bit

1 = Power-up timer is disabled

0 = Power-up timer is enabled

bit 2

WDTE: Watchdog Timer Enable bit

1 = WDT enabled

0 = WDT disabled

bit 1:0

FOSC1:FOSC0: Oscillator Selection bits

= RC oscillator

= HS oscillator

= XT oscillator

= LP oscillator

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