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• Stub connections off the main line should be avoided if possible or at least be kept as short as possible. Stub
connections must not have terminating resistors.
• Maximum cable length to 1200 m (4000 ft).
• To assure a high degree of electromagnetic compatibility and surge protection the cable should be twisted
pairs and shielded. An additional cable conductor or pair may be used for the GND reference.
Caution
Do not connect the cable shield to the GND pins! Use an external chassis ground connection
to terminate the shield.
3.8 Wiring the RS-232 interface
The RS-232 port can alternativly be used for serial communication to a Modbus Slave device instead of RS-485.
The use of the RS-232 interface must be configured using the web interface (See Section 5.3.2, "Configuring
serial line Modbus"). The SL-MOD-GW is a Modbus Master device on this interface.
The Modbus RS-232 connector is a male 9-pin D-sub type located at the bottom side of the mounted unit (refer
to Figure 2.1, "Location of connectors"). It has industry standard EIA-574 data terminal equipment (DTE) pinout
as shown in the following table and picture:
Pin
1
6
Table 3.3: Modbus RS-232 connector pinout
• Maximum cable length is 15 m (50 ft) or a length equal to a line capacitance of 2500 pF, both at the maximum
standard bit rate of 20 kbps. If operating at higher bit rates the maximum cable length drops to 3 m (10 ft)
at a bit rate of 57.6 kbps.
• To assure a high degree of electromagnetic compatibility and surge protection the RS-232 cable should
shielded. The shield shall be connected to an external chassis ground at the either or both ends, depending
on the application.
• The shield must not be connected to the GND pin.
Note
To connect the SL-MOD-GW to a PC (Personal Computer) or any other device with data
terminal equipment (DTE) pinout you need a null-modem or cross-over cable.
8
Signal
Function
1
DCD
(unused)
2
RXD
Receive data
3
TXD
Transmit data
4
DTR
(unused)
5
GND
Signal ground
6
DSR
(unused)
7
RTS
(unused)
8
CTS
(unused)
9
RI
(unused)
Direction
in
in
out
out
in
out
in
in
UMSLMODGW-1006
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