Datasheet

PIC18F6585/8585/6680/8680
DS30491D-page 26  2003-2013 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 in configuration register,
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
register details.
FIGURE 2-7: DEVICE CLOCK SOURCES
PIC18FXX80/XX85
TOSC
4 x PLL
TT1P
TSCLK
Clock
Source
MUX
Tosc/4
Timer1 Oscillator
T1OSCEN
Enable
Oscillator
T1OSO
T1OSI
Clock Source Option
for other Modules
OSC1
OSC2
Sleep
Main Oscillator
18F8680.book Page 26 Tuesday, January 29, 2013 1:32 PM