Next Revision changes

[tconrad26]

Bring out TxD2/RxD2, TxD1/RxD1, TxD0/RxD0 on separate headers.

Make them compatible with FTDI USB cables.

Make sure there's an easy way to tristate the serial drivers.

Note that the SAMD21 is not 5V tolerant, so it might be good to add buffers to protect the part where needed.

Bring out SDA1/SCL1 on header to add extra I2C port, or better yet use QWIIC connectors.

Bring +5 and +3V3 in on headers as well so we can build board without populating H1/H2 (mostly for mounting in a nice enclosure)
How would you configure the board to make it easy to put in a box?
What connectors would you choose?

If we opt to use this board in the ground station, remember that there will be another external PA. That implies either bringing out a way to break the RF path, or bring out the TX/RX signals to a header.

PAEnable was never brought out to a test header. If doing that, put SYSCLK, DCLK and DATA on it as well. This would enable a wire mode interface to the AX5043.