PIC16F7X7 datasheet(38/276 Pages) MICROCHIP

38 / 276 page

PIC16F7X7

DS30498C-page 36

 2004 Microchip Technology Inc.

4.5.1

INTRC MODES

Using the internal oscillator as the clock source can

eliminate the need for up to two external oscillator pins,

after which it can be used for digital I/O. Two distinct

configurations are available:

• In INTIO1 mode, the OSC2 pin outputs FOSC/4,

while OSC1 functions as RA7 for digital input and

output.

• In INTIO2 mode, OSC1 functions as RA7 and

OSC2 functions as RA6, both for digital input and

output.

4.5.2

OSCTUNE REGISTER

The internal oscillator’s output has been calibrated at the

factory but can be adjusted in the application. This is

done by writing to the OSCTUNE register (Register 4-1).

The tuning sensitivity is constant throughout the tuning

range. The OSCTUNE register has a tuning range of

±12.5%.

When the OSCTUNE register is modified, the INTOSC

and INTRC frequencies will begin shifting to the new

frequency. The INTRC clock will reach the new

frequency

within

8 clock

cycles

(approximately

8* 32

µs = 256 µs); the INTOSC clock will stabilize

within 1 ms. Code execution continues during this shift.

There is no indication that the shift has occurred. Oper-

ation of features that depend on the 31.25 kHz INTRC

clock source frequency, such as the WDT, Fail-Safe

Clock Monitor and peripherals, will also be affected by

the change in frequency.

OSCTUNE: OSCILLATOR TUNING REGISTER (ADDRESS 90h)

U-0

R/W-0

—

TUN5

TUN4

TUN3

TUN2

TUN1

TUN0

bit 7

bit 0

bit 7-6

Unimplemented: Read as ‘0’

bit 5-0

TUN<5:0>: Frequency Tuning bits

011111

= Maximum frequency

011110

•

000001

000000

= Center frequency. Oscillator module is running at the calibrated frequency.

111111

•

100000

= Minimum frequency

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

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