DSPIC30F datasheet(140/220 Pages) MICROCHIP

140 / 220 page

dsPIC30F5011/5013

DS70116C-page 138

Preliminary

 2004 Microchip Technology Inc.

20.2

Oscillator Configurations

20.2.1

INITIAL CLOCK SOURCE

SELECTION

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

Reset, the device selects its clock source based on:

FOS<1:0> configuration bits that select one of

four oscillator groups,

and FPR<3:0> configuration bits that select one

of 13 oscillator choices within the primary group.

The selection is as shown in Table 20-2.

TABLE 20-2:

CONFIGURATION BIT VALUES FOR CLOCK SELECTION

20.2.2

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 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 oscillator, XT, XTL, and HS

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

the primary oscillator.

20.2.3

LP OSCILLATOR CONTROL

Enabling the LP oscillator is controlled with two elements:

The current oscillator group bits COSC<1:0>.

The LPOSCEN bit (OSCON register).

The LP oscillator is on (even during Sleep mode) if

LPOSCEN = 1. The LP oscillator is the device clock if:

• COSC<1:0> = 00 (LP selected as main oscillator)

and

• LPOSCEN = 1

Keeping the LP oscillator on at all times allows for a fast

switch to the 32 kHz system clock for lower power oper-

ation. Returning to the faster main oscillator will still

require a start-up time

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

FRC w/ PLL 4x

Internal FRC

I/O

FRC w/ PLL 8x

Internal FRC

I/O

FRC w/ PLL 16x

Internal FRC

I/O

Primary

OSC2

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>).

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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