Datasheet

 1998-2013 Microchip Technology Inc. DS30289C-page 191
PIC17C7XX
17.0 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 PIC17CXXX 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 (Section 4.0)
• RESET (Section 5.0)
- Power-on Reset (POR)
- Power-up Timer (PWRT)
- Oscillator Start-up Timer (OST)
- Brown-out Reset (BOR)
• Interrupts (Section 6.0)
• Watchdog Timer (WDT)
• SLEEP mode
• Code protection
The PIC17CXXX has a Watchdog Timer which can be
shut-off only through EPROM bits. It runs off its own RC
oscillator for added reliability. There are two timers that
offer necessary delays on POR and BOR. 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 96 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.
The SLEEP mode is designed to offer a very low cur-
rent power-down mode. The user can wake from
SLEEP through external RESET, Watchdog Timer
Reset, 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 LF crystal option saves power. Configu-
ration bits are used to select various options. This con-
figuration word has the format shown in Figure 17-1.
REGISTER 17-1: CONFIGURATION WORDS
High (H) Table Read Addr. U-x R/P-1 R/P-1 U-x U-x U-x U-x U-x U-x
FE0Fh - FE08h
—PM2BODEN— — — — — —
bit 15 bit 8 bit 7 bit 0
Low (L) Table Read Addr. U-x U-x R/P-1 U-x R/P-1 R/P-1 R/P-1 R/P-1 R/P-1
FE07h - FE00h
— —PM1— PM0 WDTPS1 WDTPS0 FOSC1 FOSC0
bit 15 bit 8 bit 7 bit 0
bits 7H, 6L, 4L PM2, PM1, PM0: Processor Mode Select bits
111 = Microprocessor mode
110 = Microcontroller mode
101 = Extended Microcontroller mode
000 = Code Protected Microcontroller mode
bit 6H BODEN: Brown-out Detect Enable
1 = Brown-out Detect circuitry is enabled
0 = Brown-out Detect circuitry is disabled
bits 3L:2L WDTPS1:WDTPS0: WDT Postscaler Select bits
11 = WDT enabled, postscaler = 1
10 = WDT enabled, postscaler = 256
01 = WDT enabled, postscaler = 64
00 = WDT disabled, 16-bit overflow timer
bits 1L:0L FOSC1:FOSC0: Oscillator Select bits
11 = EC oscillator
10 = XT oscillator
01 = RC oscillator
00 = LF oscillator
Shaded bits (—) Reserved