Mr. Petkov Posted June 18, 2011 Report Share Posted June 18, 2011 Hello Dear Support Engineers, We have troubles with our RS485 network at a client site. This network was never made stable (yet). We have 3 Jazz R31, 1 V1040 and 3 MCX06D (Danfoss) in a RS485 network and we run Modbus RTU over it. We have tried 9600 and 19200 bps, 8N1, with similar success. Signal grounding is made as described in Unitronics document "Unitronics devices and RS485.pdf". The network cable we used is twisted pair, LiYCY, 2x0.75mm + shielding. Its characteristic impedance is expected to be 74 Ohms. We encounter a data loss at our single master device, the V1040 controller (Node 1). Our controller (Node 1) registers a loss of connection mostly to Node 3 and Node 7. This varies with different termination resistors we installed. We tried various termination resistor values but none is good enough to solve the data loss. We have tried to use: A) no termination at all, termination only at Node 1 and 7 (its the 150 Ohms of Unitronics devices), C) term. at Node 1 and 7 + a pair of additional external 150 Ohms to match the cable impedance of 75 Ohm. None works nice enough. What makes connection more stable is switching termination at Node 1,3,6 and 7 to ON. We hope, that with all this information you may advice us, what have we did wrong, how to workaround. Kind regards, Martin. Quote Link to comment Share on other sites More sharing options...
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