Modbus RTU and BACnet MS/TP devices are daisy-chained on an RS-485 line. For the line to work well, both ends must be terminated. On FiOC-40 and FiO-40 this is done with a small three-position switch next to the RS-485 terminal.
Which position, where?
- EOL: On the first and last device of the line.
- OFF: On every device in between.
- BIAS: Only on long lines, and only on one device in between.
Example
Consider a line with the FiOC-40 at the start, two variable frequency drives in between and an energy meter at the end. The FiOC-40 is on EOL, the drives have termination off and the energy meter has its own termination switched on. On a long line, BIAS is selected on just one of the devices in between.
Common mistakes
- Leaving termination on at every device.
- Mixing Modbus and BACnet devices on the same line; one line runs one kind of communication.
- Different communication speeds on different devices; everyone on the line must use the same setting.
Detailed technical values are given in the product datasheet; our dealers can assist you with your project.