Datasheet

PIC17C4X
DS30412C-page 100  1996 Microchip Technology Inc.
14.1 Confi
guration Bits
The PIC17CXX has up to seven configuration locations
(Table 14-1). These locations can be programmed
(read as '0') or left unprogrammed (read as '1') to select
various device configurations. Any write to a configura-
tion location, regardless of the data, will program that
configuration bit. A TABLWT instruction is required to
write to program memory locations. The configuration
bits can be read by using the TABLRD instructions.
Reading any configuration location between FE00h
and FE07h will read the low byte of the configuration
word (Figure 14-1) into the TABLATL register. The TAB-
LATH register will be FFh. Reading a configuration
location between FE08h and FE0Fh will read the high
byte of the configuration 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 configuration word in any pro-
cessor mode. See programming specifications for more
detail.
TABLE 14-1: CONFIGURATION
LOCATIONS
Bit Address
FOSC0 FE00h
FOSC1 FE01h
WDTPS0 FE02h
WDTPS1 FE03h
PM0 FE04h
PM1 FE06h
PM2
(1)
FE0Fh
(1)
Note 1: This location does not exist on the
PIC17C42.
Note: When programming the desired configura-
tion locations, they must be programmed in
ascending order. Starting with address
FE00h.
14.2 Oscillator
Configurations
14.2.1 OSCILLATOR TYPES
The PIC17CXX can be operated in four different oscil-
lator modes. The user can program two configuration
bits (FOSC1:FOSC0) to select one of these four
modes:
• LF: Low Power Crystal
• XT: Crystal/Resonator
• EC: External Clock Input
• RC: 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 specifica-
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)
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.
C1
C2
XTAL
OSC2
Note1
OSC1
RF
SLEEP
PIC17CXX
To internal
logic