Datasheet

 1997 Microchip Technology Inc. DS30444E - page 103
PIC16C9XX
14.0 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 PIC16CXXX family has a
host of such features intended to maximize system reli-
ability, minimize cost through elimination of external
components, 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)
• Interrupts
• Watchdog Timer (WDT)
• SLEEP
• Code protection
• ID locations
• In-circuit serial programming
The PIC16CXXX 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,
designed to keep the part in reset while the power sup-
ply 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-up 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.
14.1 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.
FIGURE 14-1: CONFIGURATION WORD
CP1 CP0 CP1 CP0 CP1 CP0 — — CP1 CP0 PWRTE WDTE FOSC1 FOSC0
Register: CONFIG
Address 2007h
bit13 bit0
bit 13-8 CP1:CP0 Code protection bits
(1)
5-4: 11 = Code protection off
10 = Upper half of program memory code protected
01 = Upper 3/4 of program memory code protected
00 = All memory is code protected
bit 6: Unimplemented: Read as '1'
bit 3: PWRTE: Power-up Timer Enable bit
1 = PWRT disabled
0 = PWRT enabled
bit 2: WDTE: Watchdog Timer Enable bit
1 = WDT enabled
0 = WDT disabled
bit 1-0: FOSC1:FOSC0: Oscillator Selection bits
11 = RC oscillator
10 = HS oscillator
01 = XT oscillator
00 = LP oscillator
Note 1: All of the CP1:CP0 bits have to be given the same value to enable the code protection scheme listed.