64GA106 datasheet(120/330 Pages) MICROCHIP

120 / 330 page

PIC24FJ256GA110 FAMILY

DS39905E-page 120

 2010 Microchip Technology Inc.

8.4

Clock Switching Operation

With few limitations, applications are free to switch

between any of the four clock sources (POSC, SOSC,

FRC and LPRC) under software control and at any

time. To limit the possible side effects that could result

from this flexibility, PIC24F devices have a safeguard

lock built into the switching process.

8.4.1

ENABLING CLOCK SWITCHING

To enable clock switching, the FCKSM1 Configuration

bit in CW 2 must be programmed to ‘0’. (Refer to

Section 25.1 “Configuration Bits”

for further details.)

If the FCKSM1 Configuration bit is unprogrammed (‘1’),

the clock switching function and Fail-Safe Clock Monitor

function are disabled; this is the default setting.

The NOSCx control bits (OSCCON<10:8>) do not

control the clock selection when clock switching is dis-

abled. However, the COSCx bits (OSCCON<14:12>)

will reflect the clock source selected by the FNOSCx

Configuration bits.

The OSWEN control bit (OSCCON<0>) has no effect

when clock switching is disabled; it is held at ‘0’ at all

times.

OSCTUN: FRC OSCILLATOR TUNE REGISTER

U-0

—

bit 15

bit 8

U-0

R/W-0

—

TUN5(1)

TUN4(1)

TUN3(1)

TUN2(1)

TUN1(1)

TUN0(1)

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 15-6

Unimplemented:

Read as ‘0’

bit 5-0

TUN<5:0>:

FRC Oscillator Tuning bits(1)

011111

= Maximum frequency deviation

011110



000001

000000

= Center frequency, oscillator is running at factory calibrated frequency

111111



100001

100000

= Minimum frequency deviation

Note 1:

Increments or decrements of TUN<5:0> may not change the FRC frequency in equal steps over the FRC

tuning range and may not be monotonic.

Note:

The Primary Oscillator mode has three

different submodes (XT, HS and EC)

which are determined by the POSCMDx

Configuration bits. While an application

can switch to and from Primary Oscillator

mode in software, it cannot switch

between the different primary submodes

without reprogramming the device.

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