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dsPIC30F4011/4012

DS70135G-page 154

2010 Microchip Technology Inc.

21.2

Oscillator Configurations

21.2.1

INITIAL CLOCK SOURCE

SELECTION

While coming out of Power-on Reset or Brown-out

Reset, the device selects its clock source based on:

The FOS<1:0> Configuration bits that select one

of four oscillator groups.

The FPR<3:0> Configuration bits that select one

of 13 oscillator choices within the primary group.

The selection is as shown in Table 21-2.

21.2.2

OSCILLATOR START-UP TIMER

(OST)

In order to ensure that a crystal oscillator (or ceramic

resonator) has started and stabilized, an Oscillator

Start-up Timer (OST) is included. It is a simple, 10-bit

counter that counts 1024 TOSC cycles before releasing

the oscillator clock to the rest of the system. The time-

out period is designated as TOST. The TOST time is

involved every time the oscillator has to restart (i.e., on

POR, BOR and wake-up from Sleep). The Oscillator

Start-up Timer is applied to the LP, XT, XTL and HS

modes (upon wake-up from Sleep, POR and BOR) for

the primary oscillator.

TABLE 21-2:

CONFIGURATION BIT VALUES FOR CLOCK SELECTION

Oscillator Mode

Oscillator

Source

FOS1

FOS0

FPR3

FPR2

FPR1

FPR0

OSC2

Function

Primary

CLKO

ECIO

Primary

I/O

EC w/PLL 4x

Primary

I/O

EC w/PLL 8x

Primary

I/O

EC w/PLL 16x

Primary

I/O

ERC

Primary

CLKO

ERCIO

Primary

I/O

Primary

OSC2

XT w/PLL 4x

Primary

OSC2

XT w/PLL 8x

Primary

OSC2

XT w/PLL 16x

Primary

OSC2

XTL

Primary

OSC2

Primary

OSC2

FRC w/PLL 4x

Primary

I/O

FRC w/PLL 8x

Primary

I/O

FRC w/PLL 16x

Primary

I/O

Secondary

——

(Notes 1, 2)

FRC

Internal FRC

——

(Notes 1, 2)

LPRC

Internal LPRC

——

(Notes 1, 2)

Note 1:

OSC2 pin function is determined by the Primary Oscillator mode selection (FPR<3:0>).

Note that the OSC1 pin cannot be used as an I/O pin, even if the secondary oscillator or an internal clock

source is selected at all times.

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