3.6.4. FGT PMA Fractional Mode
For a given data rate, the drop-down menu lists the supported integer mode reference clock frequencies. For a given data rate, if the required reference clock frequency is not listed in the drop-down, you can either select one of the supported integer mode reference clock frequencies or enable fractional mode.
- When enabling fractional mode, if exact fraction is not available (K = 0.25,0.5, 0.75), use 140MHz reference clock frequency for approximate fractional mode.
- To calculate K, divide k value displayed in the IP GUI system messages; K = k / 2^22. For example, for k = 2097152, K = 0.5.
- For a given data rate, you must enable fractional mode if you need to dynamically configure the K value during run time. When you enable fractional mode, you must enter the TX FGT PLL fractional mode reference clock frequency.
FGT PMA supports fractional mode in following PMA modes:
|PMA Mode||Fractional Mode Support|
|TX simplex||TX FGT PLL supports fractional mode in TX simplex. To enable, select TX simplex option for PMA mode, and turn on the Enable TX FGT PLL fractional mode in the parameter editor. The TX PLL fractional counter values automatically calculate for the selected reference clock frequency. You can place TX Simplex fractional mode on any of 16 FGT TX PMAs.
Note: FGT PMA does not support fractional mode for RX simplex.
|Duplex||FGT PMA in Duplex PMA mode supports fractional mode. To enable fractional mode in duplex PMA mode, select the Duplex option for PMA mode, select 16 for the Number of PMA lanes, and turn on Enable TX FGT PLL fractional mode option in the parameter editor.
|Primary PLL configuration||To enable fractional mode with the primary PLL configuration, select the Duplex option for PMA mode, select 2 or 4 for the Number of PMA lanes, and turn on Enable TX FGT PLL fractional mode and Enable TX FGT PLL cascade mode options in the parameter editor.