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PIC18F/LF1XK50

DS41350E-page 22

Preliminary

2010 Microchip Technology Inc.

2.6.1

OSCTUNE REGISTER

The HFINTOSC is factory calibrated, but can be

adjusted in software by writing to the TUN<5:0> bits of

the OSCTUNE register (Register 2-3).

The default value of the TUN<5:0> is ‘000000’. The

value is a 6-bit two’s complement number.

When

the

OSCTUNE

modified,

the

HFINTOSC frequency will begin shifting to the new

frequency. Code execution continues during this shift,

while giving no indication that the shift has occurred.

OSCTUNE does not affect the LFINTOSC frequency.

The operation of features that depend on the LFINTOSC

clock source frequency, such as the Power-up Timer

(PWRT), Watchdog Timer (WDT), Fail-Safe Clock Mon-

itor (FSCM) and peripherals, are not affected by the

change in frequency.

The OSCTUNE register also implements the INTSRC

and SPLLEN bits, which control certain features of the

internal oscillator block.

The INTSRC bit allows users to select which internal

oscillator provides the clock source when the 31 kHz

frequency option is selected. This is covered in greater

detail in Section 2.5.1 “LFINTOSC”.

The SPLLEN bit controls the operation of the frequency

multiplier. For more details about the function of the

SPLLEN bit see Section 2.9 “4x Phase Lock Loop

Frequency Multiplier”

REGISTER 2-3:

OSCTUNE: OSCILLATOR TUNING REGISTER

R/W-0

INTSRC

SPLLEN

TUN5

TUN4

TUN3

TUN2

TUN1

TUN0

bit 7

bit 0

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

bit 7

INTSRC: Internal Oscillator Low-Frequency Source Select bit

= 31.25 kHz device clock derived from 16 MHz HFINTOSC source (divide-by-512 enabled)

= 31 kHz device clock derived directly from LFINTOSC internal oscillator

bit 6

SPLLEN: Software Controlled Frequency Multiplier PLL bit

= PLL enabled (for HFINTOSC 8 MHz only)

= PLL disabled

bit 5-0

TUN<5:0>: Frequency Tuning bits

011111

= Maximum frequency

011110

000001

000000

= Oscillator module is running at the factory calibrated frequency.

111111

100000

= Minimum frequency

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