13.6. ×6/×N Bonded Clocking
When you specify ×6/×N bonding, the transceiver channels that reside in the same bank as the TX PLL are driven over the x6 clock line. Channels outside of the this bank are driven on the ×N clock lines, as the following figure illustrates.
Bonded clocks allow you to use the same PLL for up to 13 contiguous channels above and below the TX PLL for a total of 27 bonded channels as the following figure illustrates.
You can use the tx_clkout from any channel to transfer data, control, and status signals between the FPGA fabric and the transceiver channels. Using the tx_clkout from the central channel results in overall lower clock skew across lanes. In the FPGA fabric, you can drive the tx_clkout from the connected channel to all other channels in the bonded group. For bonded clocking, connecting more than one tx_clkout from the transceiver channel to the FPGA fabric results in a Fitter error. You can also choose the tx_pll_refclk to transfer data, control, and status signals between the FPGA fabric and the transceiver channels. Because this reference clock is also the input to the TX PLL, it has the required 0 ppm difference with respect to tx_clkout.
ATX, CMU and Fractional PLLs
For data rates above 8 Gbps, Altera recommends the ATX PLL because it has better jitter performance. Refer to "Clock Network Maximum Data Rate Transmitter Specifications" in the Stratix V Device Datasheet for detailed information about maximum data rates for the three different PLLs. The supported data rates are somewhat higher when a design specifies up to 7 contiguous channels above and below the ATX PLL rather than the maximum of 13 contiguous channels above and below the ATX PLL.
You can also use the CMU or fractional PLLs at lower data rates. If you select the CMU PLL as the TX PLL it must be placed in physical channel 1 or 4 of the transceiver bank. That channel is not available as an RX channel because the CMU PLL is not available to recover the clock from received data. Consequently, the using the CMU PLL creates a gap in the contiguous channels.
Did you find the information on this page useful?