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Simply using Modbus protocol.

This comm protocol is based on sevral type of requests to exchange datas between OPLC very simply.

- Use OPLCs serial port correctly configured with the FB provided in the VIGILOGIC Soft.

- Use the Modbus functions to Read/Write the desire datas in the slave.

Take a look in the help under communication/modbus (keep away the Modbus TCP/IP) then take a look to the programs in the samples directory :

..\Unitronics\Examples\Version 861\Project examples\Communications\MODBUS


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  • 2 years later...

Sorry I have taken so long to get back to this. This project got put on the back burner for a while. I have a Red Lion G306 Touch panel that I am using to communicate with The V230 PLC's. The G306 is set up as the Unitronics master and is writing to and reading an integer file via RS-485. The two PLC's at the end of my network (farthest from the G306 master) communicate just fine. The two nearest the G306 do not communicate at all. There is about 30 ft between the G306 and the first two PLC's and about 20 ft between the first two and the last two. On the V230 closest to the G306, SI 88 (Connection status:COM 3) is flashing -32768 while the other three V230's show 0. The V230 next to that one shows SI 85 (Error Code COM 3) as 15 while the others show 0. Any Ideas?


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My first suspicion would be that the + and - data lines got swapped on the two that are not working and then swapped back at the final node. I would double triple check the wiring.

Double Triple check that the jumper setting for the two that are not working match the RS485 setting that is on the ones that are.

Double Triple check the comm setting Baud, parity etc of the non- functioning units.

Double Triple check that you didn't accidently give two of them the same node number/ address.

Next thing to try is powering up all the slaves first, and then power up the master some time after.

Next, power the system up with one of the units that doesn't work unplugged. Does it affect the other units. Repeat with the other non-functioning unit.

Describe you wiring more. How did you daisy chain your signal from port to port physically? What type of wire are you using? How did you implement your terminating resistors?

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I am using Cat 5e cable running into and out of each device. I am using the stubs that are supplied with the communication card. I have the terminating resistors set on the last unit (UID 67). I have no other resistors on the network. I will try your suggestions and see if anything changes. Ill post my findings. Thank you.

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  • 4 weeks later...
  • MVP 2014

I have seen this happen with a water pump system. Distances were not much different to yours, but a nearby lightning strike would take it down every time, and the PLC would lose one or both on-board ports as well.

That problem was solved with V200-19-RS4-X isolated serial cards.

Hope this helps.

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  • 3 months later...

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