Texas Instruments SCAU020 - Manual (Page 7)

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3 Block Description
3.1 Block A
3.2 Block B
3.3 Block C
3.4 Block D
4 Software-Selectable Options
Block Description
This section discusses the four EVM blocks.
Block A includes a CDCE421 QFN device that accepts an LVCMOS reference input through the vertical
SMA input connector (Ref Input) which is ac-coupled onto the board.
This block includes a CDCE421 QFN device that uses an AT-cut crystal. This block can be used as either
an XO or a VCXO. For use as an XO or VCXO, the crystal should be mounted on either of the two crystal
footprints on the board. A vertical SMA input connector must also be installed on the provided footprint to
be used as the control voltage input for use as a VCXO.
Block C includes a CDCE41 device in its bare die form, packaged within a 5x7 oscillator. The oscillator
package also includes a fixed frequency crystal with a specified load and range. Oscillators with different
frequency crystals that contain a CDCE421 device can be obtained through
Pletronics.
The fourth block, D, includes a socket fitting the oscillator part used in Block C.
The provided EVM software is controlled through a graphical user interface (GUI). The software allows
users to easily send commands to the CDCE421 through the host-powered USB interface. The EVM
includes a slave USB controller that transmits the commands to the single-pin programming interface
included on the CDCE421. DC power for the USB controller can be provided either from the 5V power pin
in the USB cable or by using an external 5V ac adapter (plugged into the slot available on the EVM).
In addition to writing commands to the CDCE421 SRAM while the board is powered, software commands
can also be stored in either the nonvolatile USB microcontroller memory or the EEPROM included within
the CDCE421. This architecture allows users to start the EVM in the desired state without requiring
additional programming at power-up.
Note that the CDCE421 does have a permanent EEPROM lock mode. When this mode is selected, the
embedded EEPROM in the CDCE421 cannot be changed. This mode is useful when setting final
configurations.
SCAU020 – March 2007 10.9MHz–1175MHz Low Phase Noise Clock Evaluation Board 7
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