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If using Modbus protocol, use ASCII mode. RTU mode has tighter timing requirements that
might prevent communications while using the modem. ASCII mode is enabled by
configuration switch S1-4 in the ON position. Enable the RS-232 handshaking lines by
setting the configuration switch S1-6 to the ON position. Connect the modem to TB11 as
detailed in Figure 8. Set the baud rate to 9600 bps by setting the configuration switch S1-7
to the OFF position. Set the modem up for the settings listed on the following page.
The telephone cable plugs into a standard analog phone line. This modem will not work with
office digital phone systems. The telephone line needs to be a dedicated analog phone line
similar to most fax machines. Plug in the ac power supply. The host software needs to have
the same protocol and serial parameters as the communications option.
U.S. Robotics modem product # USR5686D (or equivalent)
Switch Position
U.S. Robotics Modem
Product No, USR5686D
(or equivalent product)
AC POWER
SUPPLY
Modem DIP Switch Settings
Setting
1
Down
Data Terminal Ready override
2
Up
Verbal result codes
3
Down
Display result codes
4
Up
Echo offline commands
5
Up
Auto answer on
6
Up
Carrier detect normal
7
Down
Load factory defaults
8
Down
Smart mode
Communications Module
PC Board (A12)
20 8
6
5
4
7
2
3
TO ANALOG
PHONE LINE
Figure 8
Modem Connection
AT Series
HARDWARE
8
13
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