Datasheet

PIC16C77X
 1999-2013 Microchip Technology Inc. Advance Information DS30275B-page 127
12.0 SPECIAL FEATURES OF THE
CPU
These PICmicro devices have a host of features
intended to maximize system reliability, minimize cost
through elimination of external components, provide
power saving operating modes and offer code protec-
tion. 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)
• Low-voltage detection
• SLEEP
• Code protection
• ID locations
• In-circuit serial programming
These devices have 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 type resets
only (POR, BOR), designed to keep the part in reset
while the power supply stabilizes. With these two timers
on-chip, most applications need no external reset cir-
cuitry.
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.
Additional information on special features is available in
the PICmicro™ Mid-Range Reference Manual,
(DS33023).
12.1 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.
Some of the core features provided may not be neces-
sary to each application that a device may be used for.
The configuration word bits allow these features to be
configured/enabled/disabled as necessary. These fea-
tures include code protection, brown-out reset and its
trippoint, the power-up timer, the watchdog timer and
the devices oscillator mode. As can be seen in
Figure 12-1, some additional configuration word bits
have been provided for brown-out reset trippoint selec-
tion.
774.book Page 127 Tuesday, January 29, 2013 12:02 PM