Distech Controls RS485 Installation Manual page 4

COM Port Usage
The Dual RS485 option adds two COM ports on the installed EC-BOS. The EC-BOS has two onboard RS485 ports. In an EC-Net 4 station running on
the EC-BOS, these two ports always operate as COM1 and COM2.
Installed serial option modules (RS485 or RS232) continue COM port numbering based on proximity to the EC-BOS, where the option module closest to
the EC-BOS base operates as the next available serial COM port(s).
For example, if attached directly to the EC-BOS, this dual RS485 option module operates as COM3 and COM4. If another dual RS485 option module is
attached to it, the second module operates as COM5 and COM6. The figure below shows a few combinations with port assignments.
Figure 3: COM port numbering examples
Wiring: Earth Ground Wiring
Earth grounding provides protection from electrostatic discharge or other forms of EMI.
Figure 4: Earth ground to option module (and EC-BOS)
4 / 7