of the adapter. Retry the ‘Connect’. If you get an error message about the COM port,
see that the supercom.dll is found in the same directory as the configuration tool, and
recheck the port number on the PC’s Device Manager. You must get “USB is
responding” followed by “Ready” or “Auto connected” before continuing.
(c) Is the Token LED on the USB adapter flickering? If not, either there is nothing on
the MS/TP network or the network has not recognized the adapter’s reply to poll for
master. If the network was online before the adapter was connected, the adapter will
wait for the token indefinitely. If no other device on the network grants the token, the
adapter will never begin communicating. Failure to get in sync, assuming all devices
appear otherwise functional, is most often caused by either a mismatch in baud rate,
mismatch in max master setting, or unusable choice of mac address.
(d) Is the PFM (poll for master) LED on the USB adapter nearly solid on? This means
the adapter is busy sending out polls for master but not seeing any response. This can
be caused by nothing being on the network, a mismatch in baud rate, or other low
level communication problems. The normal LED activity when the adapter is connected
and in sync with the network will be continuous flickering of the Token LED, usually
but not always some periodic flickering of the PFM LED, and occasional flashing of the
Data LED. The error LED could also flicker once in a while, but hopefully not often.
NOTE: The two “not really connected” indications you are most likely to see are (i)
None of the LEDs next to the terminal block on the adapter ever flash; (ii) The PFM
(yellow) LED is always flickering (nearly constant on). It is a somewhat random
coincidence whether other devices on the network or the adapter gets ahead in
polling. Devices on the MS/TP network always wait for the right opportunity to
respond. If they never get that opportunity due to being out of sync as a result of
incorrect baud rate, etc, they will appear to be “offline”. Meanwhile, a device polling to
look for other devices will constantly just poll because it is not getting any response.
Because the device doing the constant polling will generate enough traffic on the line
to make the line look busy to other devices, the other devices will never come online.
14.4 MS/TP Trouble Shooting - Device Behavior
The above discussion is focused on getting the USB to MS/TP adapter connected.
However, the situation involving one device being out of sync with the network can
happen with any device on the network. This is the situation that creates the
appearance of a single device refusing to go online, or a single device taking down the
network. If a device appears to work normally when connected to only the USB
adapter, but either refuses to go online or appears to take down the network when
connected to a running network, its port settings are out of sync with the rest of the
network. It will take a few seconds for the network to re-sync any time a new device is
added, but if the network does not return to normal token passing within a reasonable
time, the newly added device needs attention.
Trouble shooting the ValuPoint MS/TP Connection
14. Trouble Shooting
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