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DP83640 DEMO BOARD USER GUIDE
2.4
Clock Sources
The board can be configured to operate with either a crystal or an external oscillator.
2.4.1 Crystal (Default)
The board comes with a 25 MHz crystal for use in the MII configuration. A surface mount device
using the pads provided on the bottom side of the board can replace the through-hole part.
2.4.2 Oscillator
To use the board with a 25 MHz oscillator, remove the crystal (Y2) and resistors R22 and R25,
populate the oscillator (X1) and R27 with a 0 ohm resistor. The board will accept oscillators in
both full and half can package sizes.
For Reduced MII mode, two modes of operation are supported (RMII Master Mode and RMII
Slave Mode). For RMII Master Mode, the DP83640 internally generates the 50 MHz RMII
reference clock from the 25 MHz XTAL. For RMII Slave Mode operation, an external 50 MHz
oscillator must provide the reference to the X1 input of the DP83640. Refer to the DP83640
datasheet for details on configuring the device for RMII Master and Slave Modes.
