Modbus Ethernet Slave coils and discrete inputs

Hi,
I'm having serious problems in the comunication of more than 16 bits for coils or discrete inputs.
In this forum i've read some few post about this matter, tried the possible solution but got nothing working.
Guess that there is some kind of limitation or error in the ModBus modules available at the NI Labview webpages.
The idea is very simple:
I want to be able to sent 32 bits of coils from the ModBus Ethernet Master to the slave and sent 64 bits of discret inputs from the ModBus Ethernet Slave to the Master.
Can someone please give me a push? Im' kind of newbie with the Labview and would apreciate if someone that had this problem resolved could guit me a hint.
My best regards, Jorge
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Hi Jorgelopes,
thank's for posting on National Instruments forum.
Can you tell me if you want to communicate with an automate or a computer.
If you do not tried between two computer I suggestion to make the test.
Can you send the VI with which you encounter this trouble?
Best regards,
Flo
Open Diagram First

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I have the same problem with the MB Ethernet.
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How to implement Modbus Ethernet communication in Lookout, if we want to simulate the PC as PLC ?

Problem Description :
Dear Sir,
We are doing a project where we are using Lookout with
Front end Modicon PLC. The communication is by
Ethernet, using Modbus.
Since the installation is at a distant place, we wanted
to use another PC (running Lookout) to simulate the
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a: the server Lookout PC running Modbus Ethernet mode of
Modbus object as Master
b: with another PC (for simulating the PLC) running
Modbus Slave
We did not get any communication. (we have given the
details of what we have done, at the end of this email)
We also tried connecting the above 2 PC's as
a: the server Lookout PC running Modbus Serial mode of
Modbus object as Master
b: with another PC (for simulating the PLC) running
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Again we did not get any communication.
If instead of PC (b) we connect the Modbus simulator to
PC (a), there is no problem in communicating
Please let us know how to go about establishing the
communication between 2 PC's using Modbus serial,
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Thanking you
Warm Regards
Raja Mahbubani
Procedure of our trial with ethernet.
This is what we have done in detail.
On PC A:
We created an object (Pot) and connected it to
the modbus data member of the modbus object say 40001. In the
properties of the modbus object we selected modbus ethernet mode
of communication and in the IP address field we wrote the IP
address of the machine B to which we are trying to communicate
i.e. 152.63.50.2.
On PC B: we tried the following two methods
Trial 1 : We created a modbus slave object and
inserted an expression for the same data memeber to which the
object was connected hoping to get the value of the pot of machine
A on machine B.
Trial 2 : We created a modbus object on machine B and we wrote
the IP address of machine A and inserted an expression for the
same datamemeber to which the object was connected hoping to get
the value of the pot of machine A on machine B.
NI Software : Lookout
Version : 4.0.1 or 4.5
OS : Windows 98
NI Hardware : N/A
Drivers : N/A
Other Hardware/Instruments : N/A
CPU : Pentium
RAM : 64
Vendor : S-Tech
Customer Information :
Raja Mahbubani
Theta Controls
IN
[email protected]
Ph: (+91) 20 4222556/7

The ModbusSlave which comes with Lookout currently supports only Serial communication. So, you cannot use Ethernet between your two PCs. At least not with Modbus Master-Slave setup (if you must speak Ethernet between the two PCs, IPASCII object lets you do that, but then you'll need to implement your own protocol).
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Hope this helps.
Rgds,
Khalid

I need help with Modbus Ethernet communication

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Attachments:
test37.vi ‏83 KB

Hi.. and thank's for your answer..
Yes, I have downloaded and tried the modbus lib before, and it works, but I have to rebuild it to make it work good for my system..
Maybe that is the way to go.. But I also thought that when I have DSC installed, it would be easier to use that one..
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Further adventures in modbus ethernet land

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SimpleVI #3.vi ‏33 KB
Simple VI #3.JPG ‏86 KB
SimpleVI #3.lvproj ‏13 KB

Think I may have found a solution thanks to a post from a few years back.
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Working project.JPG ‏124 KB

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Solved!
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Yes, Modbus driver supports ethernet
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Forshock - Consult.Develop.Solve.

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Solved!
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Just a thought but I think the register addresses used by LabVIEW are one off of the actual register #. I was using a CRIO as a modbus IO Server and had to shift the register addresses by 1 to get things to work correctly (can;t recall if it was +1 or -1). This is documented somewhere on ni.com but can;t seem to find it now. But here is another link that may help:
http://zone.ni.com/reference/en-XX/help/371618E-01/lvmve/dsc_modbus_using/
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How can i write the floats value in Unitronics vision230 plc using modbus Ethernet

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Narendra.
Solved!
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Thanks Amit for your solution but i can not use the string to write the value because MB Ethernet master Query.vi only accepet the integer value its not take string values or any other i.e floats values etc.....otherwise i have no problem to write or read the 32 bit register values , only problem is that the MB Ethernet master Query.vi only accept the integer value there4 how can write the float value.
Narendra
Message Edited by Artemistech on 01-30-2009 11:06 PM

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Here is a Modbus master utility. Please use it to test the modbus connection.
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Modbus Ethernet Slave coils and discrete inputs

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