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Newbie 5kdaily
Registered: ‎01-21-2019

Ultrascale Select IO: RX and TX at the same bit rate with SERIAL_MODE == TRUE

Hi experts,

I'm trying to design a data interface using Select IO pins in Ultrascale, with the following requirements:

  • all pins are bidirectional, single-ended
  • RX data are read using internal fabric clock supplied by PLL, using 8x deserializers in each pin
  • TX data are transmitted also using clock from PLL, using 8x serializers
  • RX and TX rate must be the same, 800 Mb/s
  • Must use native IO primitives in order to use low-jitter PLL clock path


According to UG571, to use PLL clock for data reception RXTX_BITSLICE must have RX_DATA_TYPE set to SERIAL. In that mode, PLL clock frequency must be equal to bit rate, which is 800 MHz.

However, to transmit at the same bit rate, PLL clock must be twice the bit rate = 1600 MHz.

I cannot afford to reconfigure and then reset PLL every time I need to switch between RX and TX mode.

Is there a way to TX and RX at the same bit rate, using RX_DATA_TYPE = SERIAL?



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