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PIC17C4X

DS30412C-page 100

1996 Microchip Technology Inc.

14.1

Conguration Bits

The PIC17CXX has up to seven conguration locations

(Table 14-1). These locations can be programmed

(read as '0') or left unprogrammed (read as '1') to select

various device congurations. Any write to a congura-

tion location, regardless of the data, will program that

conguration bit. A TABLWT instruction is required to

write to program memory locations. The conguration

bits can be read by using the TABLRD instructions.

Reading any conguration location between FE00h

and FE07h will read the low byte of the conguration

word (Figure 14-1) into the TABLATL register. The TAB-

LATH register will be FFh. Reading a conguration

location between FE08h and FE0Fh will read the high

byte of the conguration 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 conguration word in any pro-

cessor mode. See programming specications 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 congura-

tion locations, they must be programmed in

ascending order. Starting with address

FE00h.

14.2

Oscillator Congurations

14.2.1

OSCILLATOR TYPES

The PIC17CXX can be operated in four different oscil-

lator modes. The user can program two conguration

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

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 specica-

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.

XTAL

OSC2

Note1

OSC1

SLEEP

PIC17CXX

To internal

logic

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