18F8680 datasheet(28/496 Pages) MICROCHIP

28 / 496 page

PIC18F6585/8585/6680/8680

DS30491C-page 26

 2004 Microchip Technology Inc.

2.6

Oscillator Switching Feature

The PIC18F6585/8585/6680/8680 devices include a

feature that allows the system clock source to be

switched from the main oscillator to an alternate

low-frequency

clock

source.

For

the

PIC18F6585/8585/6680/8680 devices, this alternate

clock source is the Timer1 oscillator. If a low-frequency

crystal (32 kHz, for example) has been attached to the

Timer1 oscillator pins and the Timer1 oscillator has

been enabled, the device can switch to a low-power

execution mode. Figure 2-7 shows a block diagram of

the system clock sources. The clock switching feature

is enabled by programming the Oscillator Switching

Enable

(OSCSEN)

bit

configuration

CONFIG1H, to a ‘0’. Clock switching is disabled in an

erased device. See Section 12.0 “Timer1 Module” for

further details of the Timer1 oscillator. See Section 24.0

“Special Features of the CPU” for configuration

FIGURE 2-7:

DEVICE CLOCK SOURCES

PIC18FXX80/XX85

TOSC

4 x PLL

TT1P

TSCLK

Clock

Source

Tosc/4

Timer1 Oscillator

T1OSCEN

Enable

Oscillator

T1OSO

T1OSI

Clock Source Option

for other Modules

OSC1

OSC2

Sleep

Main Oscillator

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