I’ve got a gateway running 7.9.20. I’m talking to a CompactLogix V20 PLC, and when i try to access a long string tag of ~400 characters, it appears as a DATA folder with individual character elements.
Is there a solution to this to access as a string? I"m using the legacy driver, this happens with both 20.012 and 20.013 PLC firmware.
I’m leaning towards installing rslinx gateway to use as the OPC server, but curious if there is a native solution (aside from get rid of the antique hardware)
I’ve seen the ideas of building a list and doing a bidirectional derived tag.
Thanks!
Aside from the derived tag idea, you could try using the v21+ driver only for this large String tag. I know that large strings can be read/written in 8.1, I think that’s also true in 7.9 (though I wouldn’t be surprised if it turned out you can only read them).
Sorry, that rung a bell. I believe I tried the non-legacy driver, and you are correct, it would read but not write. Is the 8.1 driver different and likely to work for read/write?
It's just different in that at some point we fixed writing to large strings, but I thought it was only broken for strings that were large enough to require multiple requests (larger than the CIP connection size, minus some overhead), and a 400 byte string should fit.
You can't use the 8.x driver in a 7.9 gateway though.
No, but i can stand up a 8.1 test bed and try to upgrade the project to see if that fixes.
Not a bad idea to explore upgrading anyway.
7.9 EOL is in 2 weeks, and that’s after already being extended 6 months. It was originally going to be EOL at the start of the year.
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Roger that.
On the upgrade guide, it might be useful to add an explicit note that system.tag.write will still work, it is a little unclear.
Regarding my issue, I installed a 7.9.20 test bed, restored a backup from my production server, and then upgraded to 8.1.17. After doing that; I am connected to a single PLC using both the legacy driver and the modern driver.
Using the legacy driver, all tags showed as bad. Very possible this is a PLC issue, it is an old Compact and I’ve got 2x igniton servers and a FTTM connection.
The modern driver was able to read/write my long strings, so that seems positive.
I just want to clarify that when I said only use the v21 driver for the String tags I meant that.
When connected to an older processor the driver has to use symbolic addressing, which is very slow, and you will get absolutely crap performance if you try to get all your tags from this PLC using the v21 driver.
Roger, thanks-I think I’m going to “solve” by just using RsLinx Gateway, I have a spare license that I can deploy.