This basically means that you can write to or read from the FIFO's at any speed up to 50 MHz (even though the maximum REFCLK frequency is 40 MHz). This adds flexibility for the designer.
Aside: Note however, that if you stop the TX FIFO clock, the "last" character written may remain in the FIFO input register and not be transferred to the FIFO core.
TAXI-compatible HOTLink Transceiver (Attachment below 38-02020)
200-MBaud HOTLink Transceiver (Attachment below 38-02008)