Datasheet

External Clock Operation
56F8345 Technical Data, Rev. 17
Freescale Semiconductor 37
Preliminary
The crystal and associated components should be mounted as near as possible to the EXTAL and XTAL
pins to minimize output distortion and start-up stabilization time.
Figure 3-2 Connecting to a Crystal Oscillator
Note: The OCCS_COHL bit must be set to 1 when a crystal oscillator is used. The reset condition on the
OCCS_COHL bit is 0. Please see the COHL bit in the Oscillator Control (OSCTL) register, discussed
in the
56F8300 Peripheral User’s Manual.
3.2.2 Ceramic Resonator (Default)
It is also possible to drive the internal oscillator with a ceramic resonator, assuming the overall system
design can tolerate the reduced signal integrity. A typical ceramic resonator circuit is shown in Figure 3-3.
Refer to the supplier’s recommendations when selecting a ceramic resonator and associated components.
The resonator and components should be mounted as near as possible to the EXTAL and XTAL pins.
Sample External Crystal Parameters:
R
z
= 750 KΩ
Note: If the operating temperature range is limited to
below 85
o
C (105
o
C junction), then R
z
= 10 Meg Ω
CLKMODE = 0
Crystal Frequency = 4 - 8MHz (optimized for 8MHz)
EXTAL EXTALXTAL XTAL
R
Z
R
Z
CL1 CL2