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Communications Setup
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372 SPU 780 01EMAN May 2002
Modbus Communications by Modem
Overview Controllers in remote locations can be equipped with RS-232 modems. Your
computer can then connect to the controller (by telephone, radio, or microwave
systems) using its own modem. Once the connection is established, the computer
and controller behave as if they were connected directly through a Modbus network.
You can easily configure ProWORX 32 to connect to controllers through dial-up and
dedicated-line modems. Before you begin, confirm that:
The controller is properly connected to its RS-232 modem.
Your computer is properly connected to its modem.
The modems’ DIP switches, if they have them, are set like this:
DIP Switch Settings:
After configuring ProWORX 32 to use a modem, it checks to see whether there is
an active connection each time you select a device on your network.
If it cannot find one, ProWORX 32 asks you for a phone number to dial or, if your
modem uses a dedicated line, opens a connection automatically.
If it finds a connection (or after opening one), you can choose to select a Modbus
device or close the connection and open a new one.
Use a modem connection to a controller just like a direct Modbus link. You can scan
for and attach to Modbus devices (and Modbus Plus devices, if the controller
supports Bridge Mode to allow you to connect to a Modbus Plus network) just as you
normally would.
Modem DIP Switch Setting Example: US Robotics Modem DIP
Switches (seen from back)
Data Terminal Ready Always On Switch 1 (on left): Down
Verbal Word Results Switch 2: Up
Result Code Display Enabled Switch 3: Down
Command mode local echo Switch 4: Up
Auto Answer Switch 5: Up
Carrier Detect Normal Switch 6: Up
Load Non-Volatile RAM Defaults Switch 7: Up
Use AT Command Set (Smart Mode) Switch 8 (on right): Down