Weidmuller Wireless Ethernet Modem and Device Server User Manual
13
Rev Version 1.1
2.4 Serial Connections
RS-232 Serial Port
The RS-232 serial port on the WI-MOD-xxx-E-5W is a nine pin DB-9 female connector that provides connection for
host devices as well as providing a connection point for diagnostics, field testing, and factory testing.
Communication is via standard RS-232 signals, and the WI-MOD-xxx-E-5W is configured as a DCE device.
Hardware handshaking using the CTS/RTS lines is provided. The CTS/RTS lines may be used to reflect the status of
the input buffer on the local unit.
Figure 13 shows example cable drawings for connecting to a DTE host (PC) or another DCE device (modem). A rule
of thumb for determining if a device is DCE or DTE is to look at the DB-9 connector. If the connector is female the
device is DCE, and if it is male the device is DTE. In addition, if the device functions when plugged into a computer
using a standard straight-through cable, the device is a DCE.
Figure 13 Serial Cable
DB-9 Connector Pinouts
Pin
Name
Direction
Function
1
DCD
Out
Data Carrier Detect
2
RXD
Out
Transmit Data (serial data output from DCE to DTE)
3
TXD
In
Receive Data (serial data input from DTE to DCE)
4
DTR
In
Data Terminal Ready
5
GND
Signal Ground
6
DSR
Out
Data Set Ready (always high when unit is powered on)
7
RTS
In
Request to Send
8
CTS
Out
Clear to Send
9
RI
Ring Indicator
RS-485 Serial Port
The RS-485 port provides a communication link from the WI-MOD-xxx-E-5W unit to a host device using a multi-drop
cable.
Up to 32 devices may be connected within each multi-drop network. Because the RS-485 communication medium
is shared, only one unit at a time on the RS-485 cable may send data. Therefore, communication protocols based
on the RS-485 standard require some type of arbitration. RS-485 is a multi-drop communication link or bus that
can span relatively large distances (up to 1.2 km or 4000 ft) using a balanced differential paired cable. It is
recommended that the cable be shielded or twisted pair to reduce potential RF interference.
