The USB-RS485 adapter allows devices using Modbus RTU protocol to be connected directed to Davicom units.
For example, you need to use this adapter (or equivalent) to connect the ACPM-1 power meter in RTU mode to the Davicom.
Please note that this adapter is only required for Modbus devices using RTU protocol communications, it is not required for Modbus TCP protocol communications.
When a MEXM module is already connected to a Davicom unit, then other Modbus RTU devices will connect directly through the built-in RS-485 adapter on the MEXM. See the MEXM manuel for additional details.