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Citect and NR&D

Can anyone help with this one?

At one site we are using Citect v5.42 and the latest MODNET driver to talk Modbus/TCP to an old Square-D 400-series PLC via an NR&D EPE5 module (operationally the same as an MEB).

The problem: "Digital" and "Int" data types work fine, but whenever we try to read "Real" or "Long" from the EPE5 Mailbox registers (or directly from the PLC internal registers themselves) we get a value of "0.0" and that's all.

I've looked on the Citect Knowledge Base and Article Q3628 "MODNET Driver - Incorrect Values for LONGs and REALs" correctly describes the problem but does not solve it. Citect Support are currently doing a bit of head-scratching (and not for nits either! ;-)

Has anyone come across this one before??

Thanks in advance, Cameron:-)

Reply to
Cameron Dorrough
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Getting 0.0 for REALs often means wrong format or Endians. The Square D PLCs I've met (don't have the model number to hand) used IEEE S-float in big-endian reversed word order, which is a different order from PCs and may explain things. However, for LONGs you should simply get silly values, and some REALS should be non-zero, albeit silly. Getting 0.0 for everything implies a basic problem in MODNET rather than the PLC, and you can do little more than wait for Citect to stop scratching. To while away the time you could try reading known values as two 16-bit words and tell us what you get, which will enable someone to verify the format. What value does the PLC get if you write a LONG or REAL?

Chris, I/O communications developer, ABB Switzerland

Reply to
Chris Doran

Thanks for the info, Chris - I really appreciate it. We *did* find that the version of the MODNET driver that ships with Citect v5.42 is crap.. and got a hold of the latest version which is much better.. but I don't think that is the problem.

As for the last question.. it's a good one and it is on my list to try when I get to site next week. (We don't have access to the hardware in our office anymore - it shipped yesterday! :-)

Cameron:-)

Reply to
Cameron Dorrough

Assuming you still have the software, I could supply you with a Modbus/TCP server (free :).

You could also play with the Modbus/TCP OPC client/server from

formatting link
-- they modified it to handle various endians after I pointed out to them the lack of a standard. Their sample download is also free.

Chris, ABB Switzerland

Reply to
Chris Doran

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