Hello,
Thank you for reaching out!
As for transferring Modbus data via MQTT, please refer to this article. In this case, Flespi will need to be replaced by your own MQTT solution (although Flespi is also great for testing), and the router acting as a Slave will be replaced with your own Modbus device. This is the best solution if you'd like to send data when you request it.
For sending Modbus data periodically, please refer to this question. In this case, Modbus RTU Master will need to be configured instead of Modbus TCP Master.
- what is the difference between adding a modbus serial slave in the "MODBUS SERIAL SLAVE CONFIGURATION" tab and adding a "MODBUS SERIAL DEVICE" under "MODBUS SLAVE DEVICE CONFIGURATION" inside "MODBUS SERIAL MASTER" tab.
In the Modbus Serial Master tab, slave devices will be configured. This means that the router will act as a Master and will be requesting and sending data to Modbus Slave devices.
In the Modbus Serial Slave configuration, the router itself will act as a slave. More information can be found in this article. To summarize, router parameters can be received and set, when the Modbus Serial Master device is connected to your router's RS232/RS485 port.
Keep in mind, that the only difference between Modbus Serial Master and Modbus TCP Master is the communication medium.
Let me know if any more information is needed!
Best regards,
DaumantasG