PIC18F44J10-ISLASHMLQTP datasheet(31/368 Pages) MICROCHIP

31 / 368 page

DS39682E-page 29

PIC18F45J10 FAMILY

3.4

PLL Frequency Multiplier

A Phase Locked Loop (PLL) circuit is provided as an

option for users who want to use a lower frequency

oscillator circuit, or to clock the device up to its highest

rated frequency from a crystal oscillator. This may be

useful for customers who are concerned with EMI due

to high-frequency crystals, or users who require higher

clock speeds from an internal oscillator. For these

reasons, the HSPLL and ECPLL modes are available.

The HSPLL and ECPLL modes provide the ability to

selectively run the device at 4 times the external oscil-

lating source to produce frequencies up to 40 MHz.

The PLL is enabled by setting the PLLEN bit in the

OSCTUNE register (Register 3-1).

FIGURE 3-4:

PLL BLOCK DIAGRAM

VCO

Loop

Filter

OSC2

OSC1

PLL Enable (OSCTUNE)

FIN

FOUT

SYSCLK

Phase

Comparator

HSPLL or ECPLL (CONFIG2L)

÷4

HS or EC

Mode

OSCTUNE: PLL CONTROL REGISTER

U-0

R/W-0

U-0

—PLLEN(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 7

Unimplemented:

Read as ‘0’

bit 6

PLLEN:

Frequency Multiplier PLL Enable bit(1)

= PLL enabled

= PLL disabled

bit 5-0

Unimplemented:

Read as ‘0’

Note 1:

Available only for ECPLL and HSPLL oscillator configurations; otherwise, this bit is unavailable and reads

as ‘0’.

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