A ready-made (=pre-configured) Modbus TCP to BACnet IP Slave Gateway:
https://eshop.kuhse.de/de/bacnet.html
The ADF hardware itself:
https://www.adfweb.com/Home/products/BACnet_ModbusTCP.asp?frompg=nav18_4
Or you could go through the easYview, which supports BACnet as well. You’d need to create a BACnet mapping on the easYview software.