FP 1001 optomux error

[Anonymous]

I'm dealing with an FP1001 in a RS485 network which cannot be read by
Fp Explorer. I get an error back "unexcpected character from
optomux..." I tried changing the module with a new one, with same
results. The module is the second of three along the RS485 netowrk
backbone, and the other two modules work perfectly.
Is there any chance to solve the problem?
thanks, giovanni

[Aaron_G]

Giovanni,

An "Unexpected character" message generally means that one or more of the characters in a message string was corrupted. The primary cause of this on serial lines will be improper termination or noise. For RS-485 communications, you should be using two pair twisted shielded wire, with one pair having the Tx lines and the other pair having the Rx lines. The lines should be terminated at the source (computer) and the final transceiver (last FP-1001 on the line) with 120 Ohm resistors. The resistors should be placed between Tx+ and Tx- and Rx+ and Rx- (see page 8 of the FP-1000/1001 Quick Start guide http://www.ni.com/pdf/manuals/322731e.pdf ). Note that with a multi-drop RS-485 configuration, it is recommended that a daisy chain configuration is used ra
ther than a star topology.

Regards,
Aaron