Explaination for UART through-hole pads?

[wishindo]

Near the connector for the keyboard ribbon cable, there is a set of three though-hole pads labeled Rx, Tx, and Gnd. Is this the debug serial port from the SoC before it is multiplexed with analog audio on the 3.5mm jack?

[KC9UDX]

I don't think it's multiplexed; it's switched. But I'm pretty sure you can connect there and avoid turning off the audio output.

[wishindo]

I don't think it's multiplexed; it's switched.  But I'm pretty sure you can connect there and avoid turning off the audio output.

Do you know if there is a lower speed limit or other limitation on the baud rate? Or the number of the UART so that I can look for this info in the SoC datasheet?

[KC9UDX]

I don't think you can turn it down. But the information for it is in the wiki.