
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
in
configuration
register,
CONFIG1H, to a ‘0’. Clock switching is disabled in an
register details.
FIGURE 2-7:
DEVICE CLOCK SOURCES
PIC18FXX80/XX85
TOSC
4 x PLL
TT1P
TSCLK
Clock
Source
MU
X
Tosc/4
Timer1 Oscillator
T1OSCEN
Enable
Oscillator
T1OSO
T1OSI
Clock Source Option
for other Modules
OSC1
OSC2
Sleep
Main Oscillator