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Communications – Server to Device
56 • • • • Chapter Five - Troubleshooting
When you have checked all of the above, restart the client and switch to the Server's
program window. Make sure I/O Traffic Display is on; various messages should be
appearing in the window. This indicates that the client and the Server are
communicating.
If nothing appears in the Server's window, try using WWLogger to track your error
messages. The most probable error message indicates that the item used with one or
more tagnames is unrecognized by the Server. Tagnames use specific naming
conventions when accessing data from a Server, and deviation from these
conventions can cause errors.
If a device you want data from is not available to any client software, make sure that
any device you wish to see data from is Active. The Activate checkbox in the
Server's Device Configuration dialog box determines whether client software can see
the device or not. Devices whose Activate checkbox is empty will not be available to
client programs.
This section addresses communications between the PMCS DDE Server and a
device.
When attempting to establish communication, if no data appears in the client's
window, check the WWLogger for error messages. For example, one of the most
common error messages is:
TIME-OUT COMn: DeviceName
This message indicates a problem between the Server and a device on comm port n
named DeviceName. In most cases, either the Server is not communicating through
the communication port or the device is not responding.
First, ensure that the RS-485 communication port configured for use with the topic
matches the physical port the device is connected to. Second, check for other
programs that may be accessing the port, such as other DDE Servers or terminal
monitors. Shut down any such programs. Third, verify that the communication port is
operating correctly in Windows. If the communications port is not operating
correctly, the WWLogger may show a message "Unable to Open Port."
To verify that the communication port is working properly in Windows, shut down
the Server and start the Windows Terminal program. Configure the Terminal
program to use the same communication port and settings (baud rate, parity, etc.).
Use a null-modem cable to connect to another computer's port running a Terminal
program with the same settings. See if characters can be sent between the two
computers. If you don't have two computers but the computer you are using has
another port available, connect the two communication ports, start two Terminal
programs (each set to its own port) and try communicating between them.
Alternatively, connect an external modem to the communication port in question and
see if you can dial out with it.
NOTE: Remember, two devices cannot share interrupts (IRQs). Make sure the
communication port you are using has a unique IRQ assigned.
If the communication port is working properly, look for problems on the device side.
Potential problems in this area could be, but are not limited to, cabling, baud rate,
parity, stop bits, faulty device communication port, and improper addressing of a
Modbus Concentrator or Ethernet Gateway.
DDE Server User's Guide
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