The BACnet Gateway can be easily configured as Master to other BACnet devices using the BACnet Configurator tool that both VisiLogic and UniLogic provide.

In this case Unitronics PLC will be MODBUS RS485 or TCP master and the BACnet Gateway will be BACnet master to the BACnet Slave devices: (Article -https://support.unitronics.com/index.php?/selfhelp/view-article/vision-and-bacnet-networks) 

In some cases there are applications that require Unitronics PLC to be a slave to BMS (Building management system). In this case the BACnet Gateway needs to be configured as Slave to the BMS. Also Unitronics PLC will be configured as MODBUS RS485 or TCP Slave.

The CSV configuration file needs to be edited manually. (There is no option to use the BACnet Configurator for setting the BACnet gateway as Slave).

Attached are CSV examples for TCP or RS485 connection of the Unitronics PLCs to the Gateway.

In the screenshots below you can find some details in red for the CSV configuration: