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Page 19 of 29FS-8700-66_GE-SNP Manual Page 19 of 29
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.fieldServer.com
Tel: (408) 262-2299 Fax: (408) 262-2296 Toll_Free: 888-509-1970 email: support@fieldServer.com
Appendix A. Troubleshooting Tips
• Every 2
nd
message Times Out A possible cause is that the poll frequency is so low that
the time between polls is greater than the Max Link Idle Time (of the PLC). If the time is
exceeded the connection is closed. Thus when the next poll is received by the PLC it
ignores it and hence it times out in the FieldServer. After timing out, the driver re-establishes
the connection for the next poll.
• Very slow Comms Rate A timer known as the T1 timer is the minimum time that must pass
before a response to a message can be sent. Both ends of a SNP connection have their
own T1 timer (hard coded in the driver). When a connection is made the timers are
exchanged and the larger of the two is used. The drivers T1 timer is set to a very small
number. SNP message #6 indicates the size of the T1 timer. You may need to configure the
PLC to improve communications.
• Multidrop RS-485 networks. SNP protocol specifies that their may only be one master
on a network at a time. When using nameless Nodes (Node_id=0) there may be one and
only one PLC on the connection.