Modbus RTU to BACnet MSTP Gateway | |Modbus RTU to BACnet MSTP Protocol Converter
  • This gateway can read Modbus data from your Modbus RTU devices and publish it as BACnet MSTP data.
  • It can also write to the Modbus RTU devices.
  • This gateway can also do the reverse, read BACnet MSTP data and publish it as Modbus RTU data.
  • It can also write to the BACnet MSTP devices.
In summary, this gateway can act as:

Master on the Modbus RTU network: Hence it is capable of reading data from the various Modbus slave devices and writing data to them if required.

Slave on the Modbus RTU network: You can use the gateway in this mode if you have a Modbus RTU master on the network which would be reading data from the gateway.

Client/Master on the BACnet MSTP network: Hence it is capable of reading data from the various BACnet MSTP devices and writing data to them if required.

Server/Slave on the BACnet MSTP network: The gateway can be configured to be a server of data values, hence another BACnet MSTP client can read data from the gateway and write data into the gateway.

Block Diagram

 

Scenario 1

1)      On a site you have several Schneider Ion energy meters that can provide data output on Modbus RTU.

2)      The site has a BACnet MSTP based Controller that needs the energy data from the Schneider ion meters.

3)      Since the Schneider ion meters provide data output on Modbus RTU and the controller understands only BACnet MSTP a direct data exchange is not possible.

Block Diagram

 

 

Solution:

The devices can not directly communicate with each other as they are not on the same protocol. Modbus RTU is and BACnet MSTP are Serial Protocols. You need something that will convert data from BACnet MSTP device to Modbus RTU and vice versa.

ProtoConvert’s Modbus RTU to BACnet MSTP converter will be an excellent solution for this requirement. The gateway reads data from the Energy meters on Modbus RTU. It caches this data internally and then provides it on BACnet MSTP when requested from the Controller.

 

Scenario 2

1) On the other site we have Chiller that can provide data output on BACnet MSTP.

2) The site has a PLC on Modbus RTU that needs the temperature data from thermostat on BACnet MSTP.

3)  Since the Chiller provides data output on BACnet MSTP and the PLC understands only Modbus RTU and a direct data exchange is not possible.

Block Diagram

 

 

 

Solution:

The devices can not directly communicate with each other as they are not on the same protocol. Modbus RTU is and BACnet MSTP are Serial Protocols. You need something that will convert data from BACnet MSTP device to Modbus RTU and vice versa.

ProtoConvert’s Modbus RTU to BACnet MSTP converter will be an excellent solution for this requirement. The gateway reads data from the Chiller on BACnet MSTP. It caches this data internally and then provides it on Modbus RTU when requested from the PLC.

 


An Overview of the two protocols

Modbus RTU:

ModbusRTU is a serial communication protocol that connects different devices on the same network and would make the communication between them possible.

Modbus is transmitted over serial lines between devices. The cables used for the conecction are either RS-485 or RS-232 cables. The simplest setup would be a single serial cable connecting the serial ports on two devices, a Master and a Slave.

The data is sent as series of ones and zeroes called bits. Each bit is sent as a voltage. Zeroes are sent as positive voltages and ones as negative. The bits are sent very quickly. A typical transmission speed is 9600 baud (bits per second).

 

BACNet MSTP:

MS/TP is exclusive to BACnet and can be implemented using the EIA-485 signaling standard. This is a shielded twisted-pair (STP) LAN operating at speeds from 9.6Kbit/s to 76.0Kbit/s. This LAN type is particularly suitable for single controller and low cost communications.

Like the Control and Information Protocol (CIP) used in industrial application, BACnet uses objects to represent data on a network. Objects defined by the BACnet specification include Analog Input, Analog Output, Analog Value, Binary Input, Binary Output, Binary Value, Multi-State Input, Multi-State Output, Calendar, Event-Enrollment Program, Schedule, Command, and Device.

The BACnet protocol is a completely non-proprietary open communication software standard. The standard is now controlled by the ANSI (American National Standards Institute) and ASHRAE (American Society of Heating Refrigeration and Air-Conditioning Engineers) Standard 135- 1995. In June of 1995, ASHRAE adopted BACnet as a standard for the Building Automation industry.