PIC24F32KA302-ISLASHML datasheet(116/364 Pages) MICROCHIP

116 / 364 page

PIC24FV32KA304 FAMILY

DS39995D-page 116

 2011-2013 Microchip Technology Inc.

9.1

CPU Clocking Scheme

The system clock source can be provided by one of

four sources:

• Primary Oscillator (POSC) on the OSCI and OSCO

pins

• Secondary Oscillator (SOSC) on the SOSCI and

SOSCO pins

The PIC24FV32KA304 family devices consist of

two types of secondary oscillator:

- High-Power Secondary Oscillator

- Low-Power Secondary Oscillator

These can be selected by using the SOSCSEL

(FOSC<5>) bit.

• Fast Internal RC (FRC) Oscillator

- 8 MHz FRC Oscillator

- 500 kHz Lower Power FRC Oscillator

• Low-Power Internal RC (LPRC) Oscillator with two

modes:

- High-Power/High Accuracy mode

- Low-Power/Low Accuracy mode

The primary oscillator and 8 MHz FRC sources have the

option of using the internal 4x PLL. The frequency of the

FRC clock source can optionally be reduced by the pro-

grammable clock divider. The selected clock source

generates the processor and peripheral clock sources.

The processor clock source is divided by two to produce

the internal instruction cycle clock, FCY. In this

document, the instruction cycle clock is also denoted by

FOSC/2. The internal instruction cycle clock, FOSC/2, can

be provided on the OSCO I/O pin for some operating

modes of the primary oscillator.

9.2

Initial Configuration on POR

The oscillator source (and operating mode) that is used

at a device Power-on Reset (POR) event is selected

using Configuration bit settings. The Oscillator Configu-

ration bit settings are located in the Configuration

registers in the program memory (for more information,

see Section 26.1 “Configuration Bits”). The Primary

Oscillator

Configuration

bits,

POSCMD<1:0>

(FOSC<1:0>), and the Initial Oscillator Select Configura-

tion bits, FNOSC<2:0> (FOSCSEL<2:0>), select the

oscillator source that is used at a POR. The FRC Primary

Oscillator with Postscaler (FRCDIV) is the default (unpro-

grammed) selection. The secondary oscillator, or one of

the internal oscillators, may be chosen by programming

these bit locations. The EC mode Frequency Range

Configuration bits, POSCFREQ<1:0> (FOSC<4:3>),

optimize power consumption when running in EC mode.

The default configuration is “frequency range is greater

than 8 MHz”.

The Configuration bits allow users to choose between

the various clock modes, shown in Table 9-1.

9.2.1

CLOCK SWITCHING MODE

CONFIGURATION BITS

The FCKSMx Configuration bits (FOSC<7:6>) are

used jointly to configure device clock switching and the

FSCM. Clock switching is enabled only when FCKSM1

is programmed (‘0’). The FSCM is enabled only when

FCKSM<1:0> are both programmed (‘00’).

TABLE 9-1:

CONFIGURATION BIT VALUES FOR CLOCK SELECTION

Oscillator Mode

Oscillator Source

POSCMD<1:0>

FNOSC<2:0>

Notes

8 MHz FRC Oscillator with Postscaler

(FRCDIV)

Internal

111

1, 2

500 kHz FRC Oscillator with Postscaler

(LPFRCDIV)

Internal

110

Low-Power RC Oscillator (LPRC)

Internal

101

Secondary (Timer1) Oscillator (SOSC)

Secondary

100

Primary Oscillator (HS) with PLL Module

(HSPLL)

Primary

011

Primary Oscillator (EC) with PLL Module

(ECPLL)

Primary

011

Primary Oscillator (HS)

Primary

010

Primary Oscillator (XT)

Primary

010

Primary Oscillator (EC)

Primary

010

8 MHz FRC Oscillator with PLL Module

(FRCPLL)

Internal

001

8 MHz FRC Oscillator (FRC)

Internal

000

Note 1:

The OSCO pin function is determined by the OSCIOFNC Configuration bit.

This is the default oscillator mode for an unprogrammed (erased) device.

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