Westermo RM-455U-D - Manual (Page 26)

Chapter Two Installation
Man_455U-D Rev 3.04 Page 27
2.4.2 RS232 Configuration Port
The serial port is a 9 pin DB9 female and provides configuration and diagnostics of both the
local module and of other modules in the system wile the primary RS232 port is active. This
port is wired as a DCE according to EIA-561. The following table describes the connections
required to connect to a PC serial port. The highlighted entries in this table are those essential
for operation of the Configuration port.
2.4.3 RS485 Serial Port
The RS485 port provides for communication between
the 455U-D unit and its host device using a multi-
drop cable. Up to 32 devices may be connected in
each multi-drop network.
As the RS485 communication medium is shared,
only one of the units on the RS485 cable may send
data at any one time. Thus communication
protocols based on the RS-485 standard require
some type of arbitration. RS485 is a balanced,
differential standard but it is recommended that shielded, twisted pair cable be used to
interconnect modules to reduce potential RFI. It is important to maintain the polarity of the
two RS485 wires. An RS485 network should be wired as indicated in the diagram below and
terminated at each end of the network with a 120 ohm resistor. On-board 120 ohm resistors
are provided and may be engaged by operating the single DIP switch in the end plate next to
RJ-45
Pins
Modem Function EIA-561 Signal Name
1 None Ring Indicator
2 None Data Carrier Detect
3 Input Data Terminal Ready
4 Common Signal Common
5 Output Receive Data (from Modem)
6 Input Transmit Data (to Modem)
7 None Clear to Send
8 None Request to Send
HOST 455U-D HOST
RS485 CONNECTIONS