ESP32-PoE-ISO UART1 issue

[bartgrefte]

My apologies for the kick.

@ninousf and @_AndreaS_ , did you end up solving it? Running the 16MB build of ESPEasy here, I'm trying to use the MOD-RS485-ISO with HW serial1 on GPIO's 36 (Rx) and 4 (Tx).

So far no luck.

[LubOlimex]

The way to test UART of ESP32-PoE-ISO is pretty simple, connect RX and TX (with a jumper wire with female-female connectors) and open terminal and type something and see if there is echo (e.g. what you type gets printed back). If there is echo - the UART is fine and the issue is somewhere else.

I think the issue is just wrongfully using MOD-RS485-ISO, it is not a basic bare convertor. It has a main microcontroller and own firmware, and while it can be used with Modbus or similar, it is meant to be used with own firmware and commands.

[bartgrefte]

Ah, there did my message go, a notification that it was split off to a separate topic would've helped

Well, why does the MOD-RS485-ISO manual not indicate the LED's should be on in passthrough mode? It's only listed on the wiki, the LED's where off, since they (according to the schematic in the manual) are connected to the ICSP-connector I thought the LED's being off was normal.

Turns out the MOD-RS485-ISO wasn't set to factory default before shipping, a reset solved that, but not the actual problem.

Then I took my multimeter and checked if the RS485-side was actually active (voltage measurements), no problem there.

Just now I figured out why it is not working: According to the continuity mode of my multimeter, the UEXT-pin for GPIO36/U1RXD isn't connected to anything, which the schematic (rev M) seems to confirm. While both the GPIO4/U1TXD on UEXT and the side of the board and GPIO36 on the side of the board are actually connected to the ESP32.

Can you confirm that the schematic does not contain a connection between UEXT-pin GPIO36/U1RXD and the other GPIO36 and the ESP32?

[LubOlimex]

No, but I can confirm the opposite. Let me explain why you are measuring wrong:

1. Notice how we named GPIO36 as GPI36. This is not naming error. GPIO36 can only be input which is fine for RXD. This is the way the ESP32 chip and modules were designed, some pins can only be inputs. So GPIO36 actually can't be output or serve for TXD.

2. There is D4 SCHOTTKY diode to prevent parasitic powering over the RXD pin and act as protection.

3. I have no idea where are you looking at the schematic but the connection between GPI36 and the main module is visible. Here is an excerpt with wire path circled:



I believe the issue is somewhere in the pass part of the firmware, which is probably not a real problem for you, since you can use the I2C pins, but can be a problem for somebody that doesn't have the free pins.

Meanwhile, I will try to create simple Modbus demo for Arduino IDE to demonstrate using Modbus between two ESP32-POE-ISO boards and two MOD-RS485-ISO.