Comments (1)
nagyrobi
commented on July 3, 2024
Seems like the problem is missing a Modbus termination resistor. The 120ohm resistor has to be put between the A+ and B+ wires of the bus. On longer cable runs, one should attach such resistors only at the daisy chain ends. Physically put these resistors only at the first and the last device in the chain. If there's only 2 devices on the bus, it comes natural that such resistor should be placed at both. Some factory devices have it already installed, some have a jumper/switch to enable it.
As far as I can see the transceiver module above doesn't have it.
But what I don't understand, is why when the transceiver is attached to Nodemcu ESP-32S this resistor is not needed (and works super reliable for long time), but when attached to Olimex ESP32-EVB I have to put it on, otherwise bad data appears immediately.
Analog signalization mystery I think...
from esp32-evb.
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