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# Modbus wiring

The *gateway* is designed to integrate natively into your BMS architecture, whether via a traditional serial link or on a local network.

## Serial Link: Modbus RS485 (RTU)

For connection to the field bus, the *gateway* uses a detachable screw terminal block located on its upper side. This format makes pre-wiring and maintenance easier.

The markings must be strictly followed to ensure communication:

* **A** : Non-inverting signal (Data +)
* **B** : Inverting signal (Data -)
* **GND** : Ground reference (shielding or common ground)

{% hint style="info" %}
In the event of a**communication failure** (COM LED off, controller error), **check** the possible **reversal** of wires A and B, which is the most common cause of error in RS485.
{% endhint %}

## Network Link: Modbus TCP/IP

The Modbus IP protocol requires no additional wiring.

* **Support** : Communication passes directly through the Ethernet cable (RJ45 port).
* **Configuration** : Make sure that the IP address of the *gateway* is accessible by your Modbus TCP client (Controller, Supervisor, BMS) and that the standard port (502) is not blocked.


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