Pmod guidelines

[ldoolitt]

According to How to Design a Pmod – Best Practices (by Talesa Bleything, 2017-11-29) FPGA boards like this should "include ESD protection diodes and 200-ohm series resistors on the I/O pins in order to limit short circuit currents and driver conflicts." The current Marble-Mini does not do that. This puts it in the category, also mentioned in that article, of a “high speed” Pmod port, where the Pmod pins are directly attached to the FPGA.

At least this situation should be documented. It's worth considering if we should add the series resistors and protection diodes on a future revision.