PIC18F6525/6621/8525/8621
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 the CONFIG1H Configuration register
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.
2.6
Oscillator Switching Feature
The PIC18F6525/6621/8525/8621 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 PIC18F6525/6621/
8525/8621 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:
DEVICE CLOCK SOURCES
PIC18F6X2X/8X2X
Main Oscillator
OSC2
TOSC/4
4 x PLL
Sleep
TOSC
TT1P
TSCLK
OSC1
Timer1 Oscillator
T1OSO
T1OSCEN
Enable
Oscillator
Clock
Source
T1OSI
Clock Source Option
for Other Modules
DS39612B-page 24
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
