Modbus TCP is one of the oldest networking protocols still in daily use, and it is everywhere in building management, HVAC, and industrial I/O. Cueva Control supports Modbus TCP as both a master (client) and a slave (server), letting you pull sensor data into a flow or expose relay states to a BMS.
Reading a holding register
Add a Modbus Read node to your flow. Set the device IP and port (default 502), the unit ID, function code (FC03 for holding registers), start address, and count. The node fires and stores the result in a flow variable on each execution.
Writing a coil
The Modbus Write node supports FC05 (single coil), FC06 (single register), FC15 (multiple coils), and FC16 (multiple registers). Connect it to any trigger in your flow and pass the coil address and value as node inputs or hard-coded parameters.
Modbus addresses are zero-indexed in Cueva Control. If your device documentation lists coil 1, enter address 0 in the node settings.
Using Cueva Control as a Modbus slave
Enable the Modbus Server in device settings to expose relay and GPIO states as readable coils and registers. A BMS can then poll the RELO IO8 directly without any custom integration code.