30F4013 datasheet(145/228 Pages) MICROCHIP

145 / 228 page

 2010 Microchip Technology Inc.

DS70138G-page 145

dsPIC30F3014/4013

20.2.3

LP OSCILLATOR CONTROL

Enabling the LP oscillator is controlled with two

elements:

• The current oscillator group bits, COSC<2:0>.

• The LPOSCEN bit (OSCCON register).

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

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

• COSC<2:0> = 00 (LP selected as main osc.) 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

operation. Returning to the faster main oscillator still

requires a start-up time

20.2.4

PHASE LOCKED LOOP (PLL)

The PLL multiplies the clock which is generated by the

primary oscillator. The PLL is selectable to have either

gains of x4, x8 and x16. Input and output frequency

ranges are summarized in Table 20-3.

TABLE 20-3:

PLL FREQUENCY RANGE

The PLL features a lock output which is asserted when

the PLL enters a phase locked state. Should the loop

fall out of lock (e.g., due to noise), the lock signal is

rescinded. The state of this signal is reflected in the

read-only LOCK bit in the OSCCON register.

20.2.5

FAST RC OSCILLATOR (FRC)

The FRC oscillator is a fast (7.37 MHz ±2% nominal)

internal RC oscillator. This oscillator is intended to pro-

vide reasonable device operating speeds without the

use of an external crystal, ceramic resonator, or RC

network. The FRC oscillator can be used with the PLL

to obtain higher clock frequencies.

The dsPIC30F operates from the FRC oscillator when-

ever the current oscillator selection control bits in the

OSCCON register (OSCCON<14:12>) are set to ‘001’.

The

four-bit

field

specified

TUN<3:0>

(OSCTUN<3:0>) allows the user to tune the internal

fast RC oscillator (nominal 7.37 MHz). The user can

tune the FRC oscillator within a range of +10.5%

(840 kHz) and -12% (960 kHz) in steps of 1.50%

around the factory-calibrated setting (see Table 20-4).

If OSCCON<14:12> are set to ‘111’ and FPR<4:0> are

set to ‘00101’, ‘00110’ or ‘00111’, then a PLL

multiplier of 4, 8 or 16 (respectively) is applied.

TABLE 20-4:

FRC TUNING

20.2.6

LOW-POWER RC OSCILLATOR (LPRC)

The LPRC oscillator is a component of the Watchdog

Timer (WDT) and oscillates at a nominal frequency of

512 kHz. The LPRC oscillator is the clock source for

the Power-up Timer (PWRT) circuit, WDT and clock

monitor circuits. It may also be used to provide a low-

frequency clock source option for applications where

power consumption is critical and timing accuracy is

not required.

The LPRC oscillator is always enabled at a Power-on

Reset because it is the clock source for the PWRT.

After the PWRT expires, the LPRC oscillator remains

on if one of the following is TRUE:

• The Fail-Safe Clock Monitor is enabled

• The WDT is enabled

• The LPRC oscillator is selected as the system

clock via the COSC<2:0> control bits in the

OSCCON register

If one of the above conditions is not true, the LPRC

shuts off after the PWRT expires.

FIN

PLL

Multiplier

FOUT

4 MHz-10 MHz

16 MHz-40 MHz

4 MHz-10 MHz

32 MHz-80 MHz

4 MHz-7.5 MHz

x16

64 MHz-120 MHz

Note:

OSCTUN functionality has been provided

help

customers

compensate

for

temperature effects on the FRC frequency

over a wide range of temperatures. The

tuning step size is an approximation and is

neither characterized nor tested.

Note:

When a 16x PLL is used, the FRC

frequency

must

not

tuned

frequency greater than 7.5 MHz.

TUN<3:0>

Bits

FRC Frequency

0111

+10.5%

0110

+9.0%

0101

+7.5%

0100

+6.0%

0011

+4.5%

0010

+3.0%

0001

+1.5%

0000

Center Frequency (oscillator is

running at calibrated frequency)

1111

-1.5%

1110

-3.0%

1101

-4.5%

1100

-6.0%

1011

-7.5%

1010

-9.0%

1001

-10.5%

1000

-12.0%

Note 1: OSC2 pin function is determined by the

Primary

Oscillator

mode

selection

(FPR<4:0>).

2: 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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