PIC16F84A datasheet(123/337 Pages) MICROCHIP

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DS30234D-page 123

PIC16C6X

13.0

SPECIAL FEATURES OF THE

CPU

What sets a microcontroller apart from other proces-

sors are special circuits to deal with the needs of real-

time applications. The PIC16CXX family has a host of

such features intended to maximize system reliability,

minimize cost through elimination of external compo-

nents, provide power saving operating modes and offer

code protection. These are:

• Oscillator selection

• Reset

- Power-on Reset (POR)

- Power-up Timer (PWRT)

- Oscillator Start-up Timer (OST)

- Brown-out Reset (BOR)

• Interrupts

• Watchdog Timer (WDT)

• SLEEP mode

• Code protection

• ID locations

• In-circuit serial programming

The PIC16CXX 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 pro-

vides a ﬁxed delay of 72 ms (nominal) on power-up

only, designed to keep the part in reset while the power

supply stabilizes. With these two timers on-chip, most

applications need no external reset circuitry.

SLEEP mode is designed to offer a very low current

power-down mode. The user can wake from SLEEP

through external reset, Watchdog Timer Wake-up or

through an interrupt. Several oscillator options are also

made available 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 various options.

13.1

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 pro-

gram memory location 2007h.

The user will note that address 2007h is beyond the

user program memory space. In fact, it belongs to the

special test/conﬁguration memory space (2000h -

3FFFh), which can be accessed only during program-

ming.

Applicable Devices

61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67

Applicable Devices

61 62 62A R62 63 R63 64 64A R64 65 65A R65 66 67

FIGURE 13-1: CONFIGURATION WORD FOR PIC16C61

—

CP0

PWRTE WDTE FOSC1 FOSC0

CONFIG

Address

2007h

bit13

bit0

bit 13-5: Unimplemented: Read as '1'

bit 4:

CP0: Code protection bit

1 = Code protection off

0 = All memory is code protected, but 00h - 3Fh is writable

bit 3:

PWRTE: Power-up Timer Enable bit

1 = Power-up Timer enabled

0 = Power-up Timer disabled

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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