Evaluation Kit for CMX838 Family Radio Processor
11
EV8380 User Manual
4 General Notes
4.1
Baseband Clock Generation
The CMX838 offers considerable flexibility in the choice of clock sources. Baseband circuits on the CMX838
can receive their clock from any of the system RF reference oscillator (i.e. VC/TCXO), a dedicated crystal
oscillator or an externally applied clock signal of suitable frequency and amplitude.
4.1.1 Using the RF Reference Oscillator as the CMX838 Clock Source
The desired mode of CMX838 operation involves the derivation of the baseband clocks from an external RF
reference oscillator. When the device is operated in this manner, all CMX838 circuits (RF and baseband) are
synchronized to the same clock signal. Eight different RF reference oscillator frequencies, from 4.0MHz to
21.25MHz, are available for CMX838 baseband clock generation (please refer to CMX838 data bulletin for
details on available frequencies).
To operate the CMX838 with an RF reference oscillator as its baseband clock source:
1) Connect an external RF reference oscillator to connector SM3 on the EV8380 board.
Please note that the reference oscillator frequencies compatible with the CMX838 are listed in the CMX838
data bulletin.
2) Write a data byte to the SYNTHESIZER BASEBAND CLOCK CONTROL ($89) register to configure
the CMX838 clock generation circuits.
For example, if the external RF reference oscillator operates at 12.8MHz, a byte of $90 will enable baseband
clock generation from the external 12.8MHz reference oscillator.
When the CMX838 is operated with an RF reference oscillator as its baseband clock source, the normal
mode of operation for the CMX838 on-chip crystal amplifier is ‘disabled’.
4.1.2 Using External Sources as the CMX838 Clock Source
If it is not desirable to use the RF reference oscillator as the device clock source, the CMX838 can develop its
baseband clock from an external clock source; a crystal oscillator or a system clock signal can be used in this
situation. Eight different frequencies, from 4.0MHz to 24.0MHz, are available for CMX838 baseband clock
generation when operated in this manner (please refer to CMX838 data bulletin for details on available
frequencies).
4.1.2.1 Operating the CMX838 from a Crystal Oscillator
To operate the CMX838 with an external crystal oscillator:
1) Connect crystal of desired frequency to the ‘X1’ socket on the EV8380.
a. The EV8380 board is shipped from the factory with a 4.0MHz crystal.
b. If a different crystal frequency is desired, please consult the CMX838 data bulletin for other
supported crystal frequency choices.
c. Please consult the CMX838 data bulletin for recommendations concerning crystal type, drive
levels, etc.
2) Ensure jumpers E1 and E2 are installed.
3) Write a byte to the SYNTHESIZER BASEBAND CLOCK CONTROL ($89) register to configure the
CMX838 clock generation circuits.
a. For example, if the crystal operates at 4.0MHz, a byte of $40 will enable baseband clock
generation from the 4.0MHz crystal oscillator.
¤2001 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054
Doc. # 20480230.001
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