this post was submitted on 21 Jun 2023
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SBC UART debug troubleshooting (discuss.tchncs.de)
submitted 2 years ago by MaximGun@discuss.tchncs.de to c/askelectronics@discuss.tchncs.de
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Right to the point: On a BPI-R3, should connecting the UART debug pins directly to the appropriate pins on a DB9 USB serial adapter (rx->tx, tx->rx, gnd->gnd) work? Because I’m just getting a garbled mess in my serial console. I’ve tried all different baud rates. I’m using a high quality serial adapter (Keyspan Tripp Lite). I’ve tried on Linux and Windows. I assume I’m missing something stupid.

To make matters more annoying, I have a $5 almost certainly counterfeit USB serial adapter with USB on one end and DuPont connectors on the other end and it works fine, so at this point my problem is mostly academic. I would like to know what I’m doing wrong, though.

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[–] Susan_B_Good@discuss.tchncs.de 3 points 2 years ago

You probably have already sussed this - but:

DuPont connectors equates to logic level signals. There may even be a 3.3 v <>5v link selector on the adapter.

Whereas DB9 equates to "RS232" level signals. Generally, at least the capability to accept those voltage levels, even if not necessarily producing them.

My first step tends to be to connect tx to rx and see if characters typed in a terminal/emulator get echoed.

An RS232 breakout box is pretty much a given necessity, when it comes to sorting out what's happening on all those pins and sorting out what to connect to what.