In order to use all 8 UART peripherals, it seems that UART1 cannot avoid GPIO#09. U1Rx can be multiplexed to PQ4, but U1Tx can only be used on PB1 where it would be affected by GPIO#09.
Unfortunately, the only workarounds are to use the pins for USB0 or to ground them, but nothing is offered as a solution when the pins are needed for UART1.
What sort of external circuitry is needed to prevent GPIO#09 errata? Would a series resistor be enough to prevent exceeding the 2V/ns limit? If my math is right, that's 2kV/us, which seems more like ESD than normal serial data transitions.
As another potential workaround, would ESD protection on the traces leading to the UART connector be enough avoid errata GPIO#09?
Thanks for any recommendations. We're currently grounding those pins as suggested in the 1st workaround, but would prefer to open them up for UART1 use in future revisions.
