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COM128 Installation and Operation Manual Schneider Electric
8
4.2.3 CONNECTION TO A MODEM
PORT SELECTION
A telephone or radio modem typically acts as a DCE RS-232
device. Therefore, the modem’s RS-232 port should be
connected to the COM128’s DTE RS-232 port. Refer to Figure
4.2.3.
SWITCH SETTINGS
To properly communicate with the modem, the COM128 must
be configured as a DTE RS-232 device .
If the modem requires RTS-CTS handshaking, the RTS/CTS
Flow Control function provided by the COM128 should be
enabled. This will force the COM128 to buffer all RS-485 data
received until the modem is ready to receive the data. Most
radio modems require this mode, as do some telephone
modems. Refer to your modem’s operation manual to see if
your modem provides or requires this handshaking. .
Refer to Section 3.2, 'Mode Descriptions', for examples of
switch settings for this application.
IBM PC
RS-232 Cable
50 ft. max.
Telephone, Radio, or
Fibre Optic Modems
Telephone
Network, Radio or
Fibre Optic Link
RS-232
Cable
50 ft. max.
SHLD
PORT C
PORT D
PORT B
PORT A
DCE
PORT
DTE
PORT
RS-232
RS-485
COM128
RS-232 to RS-485 Converter
To
RS-485
Bus
RS-485 Cable
22 AWG shielded twisted pair.
Total length: 4000 ft. maximum.
Figure 4.2.3 RS-232 Connection to Modem