LabVIEW Modbus HELP!

[Matthew_Kelton]

Did you add the resistors because the diagram in the reference showed resistors or because the controller manufacturer said they needed to be added?  Typically, you won't need to add the resistors, as they are built in to the hardware.  Some controllers have the ability to turn them on or off so you can daisy chain multiple devices together.

[Marc Blumentritt]

Hi,

I added the resistor, because it was in the wiring guide. But I forgot to write, that I did try the communication without the resistor and again got no answer.

Marc

[Matthew_Kelton]

Do you have a link to the user manual of the controller.  I fnot, can you give me the part number so I can look it up.

[Marc Blumentritt]

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Matthew Kelton wrote:
Do you have a link to the user manual of the controller.  I fnot, can you give me the part number so I can look it up.

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I had only the German version, therefore I had to Google a little bit. I found it here in English:

http://instrumentation-central.com/WestManual/6100PlusManual.pdf

Marc

[Matthew_Kelton]

So, I am assuming you have LabVIEW setup to match the parameters setup on p42 of the manual you linked to.  If you're just using the defaults in the manual, you may wish to confirm via the controller that the settings match what you have in LabVIEW.  If you are trying to write a register value, make sure you have the write enable on p 43 turned on.  Make sure you are using the right address.  The controller doesn't respond to address 0.

Also note on p93 and p99 that some serial settings are not changeable and differ between using Modbus and ASCII.

I don't see anywhere where the termination is mentioned, so I am not sure what to tell you about the termination resistor.

[Marc Blumentritt]

Your assumptions are right. I did set up LabVIEW according to the handbook and the pages you mentioned. I did connect the TXD+ and TXD- pins according to p26 (TXD+ to 12 and TXD- to 11).

Do have any other ideas?

Oh, and thanks for your help. It is very appreciated!

Marc

[Matthew_Kelton]

That might be your problem.  You still need to connect the RX+/-.  Refer to here.  It's from the Quick Reference Guide, but explains the wiring:

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 In 2-wire transmission (half- duplex), TXD+ and RXD+ on the master are wired together to TXD+ and RXD+ on the slave(s). TXD- and RXD- on the master are wired together to TXD- and RXD- on the slave(s).

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[Marc Blumentritt]

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Matthew Kelton wrote:

That might be your problem.  You still need to connect the RX+/-.  Refer to here.  It's from the Quick Reference Guide, but explains the wiring:

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 In 2-wire transmission (half- duplex), TXD+ and RXD+ on the master are wired together to TXD+ and RXD+ on the slave(s). TXD- and RXD- on the master are wired together to TXD- and RXD- on the slave(s).

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Well, thanks!

This looks like it could solve my problem! I will try it as soon as possible and will post my results here. But it could take until next year, because I have no access to a controller at the moment 😞

Marc

[Marc Blumentritt]

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Matthew Kelton wrote:

That might be your problem.  You still need to connect the RX+/-.  Refer to here.  It's from the Quick Reference Guide, but explains the wiring:

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 In 2-wire transmission (half- duplex), TXD+ and RXD+ on the master are wired together to TXD+ and RXD+ on the slave(s). TXD- and RXD- on the master are wired together to TXD- and RXD- on the slave(s).

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Hi,

many thanks to you. I got my hands on a controller today. The communication with the it is now working.

How do I mark your message as a solution?

Mary Christmas

Marc

[Matthew_Kelton]

You should see solution icons on the right side of the repsonses to the thread.  Just click on the icon in the answer you consider the solution.