Distech Controls RS232 Installation Manual page 4

COM Port Usage
The RS232 option adds one COM port on the installed EC-BOS. The EC-BOS has two integral 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 (RS232 or RS485) 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 RS232 option module operates as COM3. If another RS232 option module is attached to it, the sec-
ond module operates as COM4. The figure below shows a few combinations with port assignments.
Figure 3: COM port numbering examples
Wiring: Earth Ground Wiring
Other than the EC-BOS ground, no ground is required on the module.
Pinout Reference
DB9M (male or plug)
Standard DB9 serial cables may be used—for example, a "null modem" cable to communicate to another DTE device. Shielded type cables are recom-
mended, with a typical maximum length of 50 feet (15.2m).
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Signal DB-9 Plug Pin
DCD 1
RXD 2
TXD 3
DTR 4
GND 5
DSR 6
RTS 7
CTS 8
not used 9