16F819 datasheet(38/176 Pages) MICROCHIP

38 / 176 page

PIC16F818/819

DS39598E-page 36

 2004 Microchip Technology Inc.

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 fre-

quency. 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 execu-

tion continues during this shift. There is no indication that

the shift has occurred. Operation 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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