PC Engines APU COM2 port?


The APU boards have a COM2 port on them, which I believe is 3V3. I was wondering of the serial console messages are also sent to that port along with the main DB9 port ?
I was wondering if one can use a ESP-01 on this port for remote serial debug.

I have successfully added a ESP-01 on the AP (Comfast). I have flashed ESPTerm on the ESP-01, can can do serial debug on that board.

Is anyone using the COM2 on the APU boards ?
[ https://pcengines.ch/schema/apu4c.pdf ]


Any comments appreciated..

Typical ESP-01 wiring..

Any second port should be available for applications as for example /dev/ttyS1. The kernel will have opened only the first port for logs and console access.

Since a TTL style port idles with the TX line high, you can measure the voltage at the TX pin to determine the logic level needed.


The APU manual seems to say COM2 is 3.3V for all the models...

Yet, I found this...

Looks like he observes that the COM2 port is 5V, instead ??