Scott Gilbertson

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Scott Gilbertson last won the day on April 18 2016

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  1. That much I've figured out. JB and JC on the Arty are high-speed (no series resistors). I had no problems running 280MHz single-ended LVCMOS33 from JB to an LVDS driver chip. See section 10.2 High-Speed Pmod, here: You can also use the Arduino/ChipKIT shield connectors. You can get an XDC file here: Un-comment the connectors you're using. You can often remove the IO standard definitions from the XDC, and let Vivado figure it out. If you use a SelectIO Interface Wizard, for example, it lets you pick which differential signaling standard to use. If you're only using part of, say, the shield connectors, I've found what works well is to write a custom VHDL/Verilog wrapper, outside the generated block-diagram wrapper, just to adapt the block diagram interface names to the actual pin names. That way you don't have to mess with the XDC file every time you change some little thing in the I/O definitions.
  2. Digilent, if you're planning to make a new revision of the Arty, please consider allowing LVDS_25 for high-speed differential output. The Artix 7 doesn't have an "LVDS_33" I/O option, so you need a 2.5V I/O bank if you want LVDS output. As far as I can tell all the I/O banks on the Arty are hardwired to 3.3V, so you can read, say, FPD-Link LVDS data, but you can't drive an LVDS display without an external driver chip, and that means sending hundreds-of-MHz single-ended signals to the driver. I think the ports in question would be those on the JB & JC connectors, because those are the two high-speed PMOD ports. A jumper to switch those to 2.5V would be great. Maybe some of the Arduino & ChipKit pins too.