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PIC17C75X Datasheet, PDF (177/320 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM Microcontrollers | |||
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PIC17C75X
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 reli-
ability, minimize cost through elimination of external
components, 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
shutoff only through EPROM 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 Oscil-
lator 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 ï¬xed
delay of 96 ms (nominal) on power-up only, designed to
keep the part in RESET while the power supply stabi-
lizes. 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 ï¬t the applica-
tion. The RC oscillator option saves system cost while
the LF crystal option saves power. Conï¬guration bits
are used to select various options. This conï¬guration
word has the format shown in Figure 17-1.
FIGURE 17-1: CONFIGURATION WORDS
U-x
R/P - 1 R/P - 1 U - x
â
PM2 BODEN â
bit15 bit 8 bit 7
U-x
â
U-x
â
U-x
â
U-x
â
U - x High (H) Table Read Addr.
â FE0Fh - FE08h
bit 0
U-x
U-x
â
â
bit15 bit 8 bit 7
R/P - 1 U - x R/P - 1 R/P - 1 R/P - 1 R/P - 1 R/P - 1 Low (L) Table Read Addr.
PM1 â PM0 WDTPS1 WDTPS0 FOSC1 FOSC0 FE07h - FE00h
bit 0
bit 6H
BODEN: Brown-out Detect Enable
1 = Brown-out Detect circuitry is enabled
0 = Brown-out Detect circuitry is disabled
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
bits 2L:3L
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 overï¬ow timer
bits 1L:0L
FOSC1:FOSC0, Oscillator Select bits
11 = EC oscillator
10 = XT oscillator
01 = RC oscillator
00 = LF oscillator
â
Reserved
© 1997 Microchip Technology Inc.
Preliminary
DS30264A-page 177
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