modbus ethernet connection help

[acolbourn]

Hey, so I've been trying for a few days to connect to an Omega ir2c series with modbus over ethernet but I'm completely stumped.  A picture of my program is attached, as well as the error I get when I hit stop.  Currently when I hit run it looks like I just keep getting an error in "TCP Write in MB Ethernet Transmit".  I wasn't exactly sure on what parameters to use but currently my starting address is 39 because the address in the manual (below) is 27 and I converted it to decimal because it looks like that was hex.  I followed peoples suggestions in other threads and tried 39, 38, 40, 27, 26, and 28 with the same results.  The other thing I was not sure about is transaction id.  As best I can tell from other people on the interenet this is usually 1 but could this be my problem?  Also, I am able to log data in excel using a macro they supplied for iseries communication so I know the device is connected properly.  When I open a connection in MAX it says it successfully opened a visa session but there is a little warning exclamation point over the device for some reason.  I'm using ip address : 192.168.1.201 on port 1000. 

Here is the communication manual for the device:  http://www.omega.com/Manuals/manualpdf/M4911.pdf

Normal manual in case:  http://www.omega.com/Manuals/manualpdf/M3752.pdf

Any help would be greatly appreciated.  Thanks in advance,

Alex

[acolbourn]

update:  I think I have established communication now by opening up a web browser and typing in the ip address.  Then I had to change an option to enable modbus despite doing this on the device already.  Also, my port had to be 2000 instead of 1000 ( I think the provided software uses 1000 and blocks modbus from using it).  Now I'm getting modbus exception code 3 (which sadly I'm excited about because at least something is happening).  If anyone knows how to fix it I'd appreciate it.  Thanks

[acolbourn]

yet another update:

It appears that changing the "Number of Connections" setting from 0 to 1 is what allows me to get the exception error 3.  If it's set to 0 then I get the Modbus write error from before.  Still have no idea how to get passed this exception error though.

[Ben-N]

Hi Alex,

Have you looked through any of the documentation on our website for MODBUS communication over ethernet?  In paritcular, section 2 and 3 of Developer Zone: Introduction to MODBUS.  There is some good documentation on the setting up your MODBUS master, and using bound variables.  Addtionally, there is some discussion about how the I/O Server is involved with this process.