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PIC17C4X Datasheet, PDF (100/240 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller | |||
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PIC17C4X
14.1 Conï¬guration Bits
The PIC17CXX has up to seven conï¬guration locations
(Table 14-1). These locations can be programmed
(read as '0') or left unprogrammed (read as '1') to select
various device conï¬gurations. Any write to a conï¬gura-
tion location, regardless of the data, will program that
conï¬guration bit. A TABLWT instruction is required to
write to program memory locations. The conï¬guration
bits can be read by using the TABLRD instructions.
Reading any conï¬guration location between FE00h
and FE07h will read the low byte of the conï¬guration
word (Figure 14-1) into the TABLATL register. The TAB-
LATH register will be FFh. Reading a conï¬guration
location between FE08h and FE0Fh will read the high
byte of the conï¬guration word into the TABLATL regis-
ter. The TABLATH register will be FFh.
Addresses FE00h thorough FE0Fh are only in the pro-
gram memory space for microcontroller and code pro-
tected microcontroller modes. A device programmer
will be able to read the conï¬guration word in any pro-
cessor mode. See programming speciï¬cations for more
detail.
TABLE 14-1: CONFIGURATION
LOCATIONS
Bit
Address
FOSC0
FE00h
FOSC1
FE01h
WDTPS0
FE02h
WDTPS1
FE03h
PM0
FE04h
PM1
PM2 (1)
FE06h
FE0Fh (1)
Note 1: This location does not exist on the
PIC17C42.
Note:
When programming the desired conï¬gura-
tion locations, they must be programmed in
ascending order. Starting with address
FE00h.
14.2 Oscillator Conï¬gurations
14.2.1 OSCILLATOR TYPES
The PIC17CXX can be operated in four different oscil-
lator modes. The user can program two conï¬guration
bits (FOSC1:FOSC0) to select one of these four
modes:
⢠LF:
⢠XT:
⢠EC:
⢠RC:
Low Power Crystal
Crystal/Resonator
External Clock Input
Resistor/Capacitor
14.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT or LF modes, a crystal or ceramic resonator is
connected to the OSC1/CLKIN and OSC2/CLKOUT
pins to establish oscillation (Figure 14-2). The
PIC17CXX Oscillator design requires the use of a par-
allel cut crystal. Use of a series cut crystal may give a
frequency out of the crystal manufacturers speciï¬ca-
tions.
For frequencies above 20 MHz, it is common for the
crystal to be an overtone mode crystal. Use of overtone
mode crystals require a tank circuit to attenuate the
gain at the fundamental frequency. Figure 14-3 shows
an example of this.
FIGURE 14-2: CRYSTAL OR CERAMIC
RESONATOR OPERATION
(XT OR LF OSC
CONFIGURATION)
OSC1
C1
XTAL
RF
SLEEP
OSC2
Note1
C2
PIC17CXX
To internal
logic
See Table 14-2 and Table 14-3 for recommended
values of C1 and C2.
Note 1: A series resistor may be required for AT strip
cut crystals.
DS30412C-page 100
© 1996 Microchip Technology Inc.
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