Modbus remains a popular network interface. It is commonly found on jobs such as boiler control, variable speed drives, and metering applications, but these devices lack BACnet compliance. To make Modbus devices appear as individual BACnet devices a BASgatewayLX is used. This device has one 10/100 Mbps Modbus TCP or BACnet/IP Ethernet port and an opto-isolated Modbus EIA-485 serial port for Modbus RTU or Modbus ASCII devices.
Up to 30 Modbus serial devices (represented by up to 1000 polled points) can share the single Modbus port on the BASgatewayLX. The virtual routing feature in the BASgatewayLX allows each connected Modbus device to appear as an individual BACnet- compliant device. What is needed is a device profile for each Modbus type device. Contemporary Controls maintains a library of common device profiles. If one is not available, Contemporary Controls will provide it upon request. Custom device profiles can be uploaded to the BASgateway.
Using web pages and a resident database of common Modbus device profiles, Modbus data points from Modbus Serial or Modbus TCP devices can be mapped to BACnet objects.
The BASgatewayLX is housed in a metal case that mounts on 35-mm DIN-rail and it is powered from a 24 VAC/VDC (± 10%) source. Its half-wave rectified power supply allows sharing of power with other half-wave devices.
The optically-isolated serial port allows for connection to either 2-wire or 3-wire EIA-485 networks using a removable 5-pin terminal block. Up to 30 EIA-485 Modbus devices can share the serial bus at data rates between 2.4 and 115.2 kbps. Internal jumpers allow flexible bias and termination options. They can be removed for mid-span installations.
The Ethernet port offers a shielded RJ-45 connector. Through auto-negotiation and Auto-MDIX, it automatically matches connections to the attached equipment. Therefore, either CAT5 straight-through or crossover cable can be used to attach to the BACnet/IP or Modbus TCP network at either 10 or 100 Mbps speed.
A resident web server allows for commissioning, and troubleshooting via a standard web browser. A reset switch is provided for returning to the factory default IP address. LED indicators provide communication status on both the Ethernet and serial ports.
