A great solution/s to interconnect Modbus RS485 devices on BACnet MSTPnetwork.

Modbus RS485

Modbus RTU is a serial communication protocol. At the physical layer Modbus RTU can work on RS232 or RS485 based communication links. Modbus RTU works on a Client/Server architecture. There can be only one Client on a Modbus RTU network. The Client initiates the poll and the Servers respond to the Client’s request. If an RS232 based topology is used there can be only one Server connected to the Client. However if RS485 based topology is used it is possible to daisy chain up to 31 Servers and connect to the Client.

ProtoConvert can supply and support gateways that can have a Modbus RTU Client or a Server interfaces.

When a gateway is configured as a Modbus RTU Client it would keep reading data from the field devices using Modbus RTU protocol. It will also be possible to program the gateway to relay commands to the field device/s. Hence when used as a Modbus RTU Client the gateway reads data from Modbus RTU Servers like power meters, UPS’, PDUs, CRAC units and makes the data available on a variety of other protocols like BACnet, SNMP , LonWorks and many others.

When a gateway is configured as a Modbus RTU Server it can be connected to a Modbus RTU Client and be a source of data. It would respond to the polls from the Modbus Client and publish the data as per the internal configuration. Hence by using the gateway as a Modbus RTU Server it is possible to publish data from other protocol networks on the Modbus RTU network for the Client/PLC/SCADA to consume.

BACnet MSTP

BACnet MSTP (Master-Slave/Token-Passing) is a communication protocol used in building automation systems to enable the exchange of data between devices such as HVAC systems, lighting controls, and access control systems. It is a simple and robust protocol that uses a token-passing mechanism to ensure that only one device can transmit data at a time. MSTP operates over a twisted pair wiring with RS-485 electrical specifications. MSTP supports both point-to-point and multi-drop network topologies and can be used for communication over long distances. BACnet MSTP is widely adopted in building automation systems and is an important part of the BACnet standard.

ProtoConvert can supply and support gateways that can have a BACnet MSTP client or server interfaces.

When a gateway is configured as a BACnet MSTP Client it would keep reading data from the field devices using BACnet MSTP protocol. It will also be possible to program the gateway to relay commands to the field devices (if protocol implementation supports, please check datasheet for details). Hence when used as a BACnet MSTP Client the gateway reads data from BACnet MSTP Servers and makes the data available on a variety of other protocols like Modbus, BACnet, SNMP, LonWorks and many others.

When a gateway is configured as a BACnet MSTP Server it can be connected to a BACnet MSTP Client and be a source of data. It would respond to the polls from the BACnet MSTP Client and publish the data as per the internal configuration. Hence by using the gateway as a BACnet MSTP Server it is possible to publish data from other protocol networks on the BACnet MSTP network.

Modbus RS485 and BACnet MSTP datasheets are available for your review on this link for detailed information on the capabilities of these drivers.

The table below lists the various hardware options available with this protocol driver combination, please make a selection based on the point capacity, number of ports, and type of communication interfaces you require.