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  1. johncrummy
  2. PLCnext Technology & PLCnext Controls
  3. Wednesday, 21 July 2021
I've just installed PLCnext Engineer 2021.6, and since writing a project to the PLC, I can no longer read any variables marked as 'Constant' in the variables work sheet via the REST API. I have not upgraded the firmware running on the PLC, it is at 2021.0.5 LTS.

Variables marked as 'Constant' return `null` as their value. If I uncheck 'Constant', I get the expected variable value.

Is this a known issue?

Frank PLCnext Team Accepted Answer Pending Moderation
Hi John,

I've just performed for myself some tests and this is in deed not working anylonger with PLCnext Engineer 2021.6.
Projects created with 2021.0.3 does allow calls to consts, but if deployed with 2021.6 it does not allow anylonger access. This issue is not related to the Firmware.

I've reported this as a defect. Thanks for sharing this with us!!

Phoenix Contact Electronics Headquarter - PLCnext Runtime Product Management and Support
johncrummy Accepted Answer Pending Moderation
Thank you, Frank.

I ended up reverting back to 2021.0.1 (I still haven't updated to the latest LTS) because I was running into some other issues as well that also appeared to be because of constants. I use a set of global constants as a set of messages that can be passed between different systems (the constants are integer values, so 1 might mean "start", 2 might mean "stop", etc.). In the program deployed with 2021.6, it seemed like a bunch of those constants were being set to 0. Deploying the exact same program with 2021.0.1 ran correctly. Sorry that this description is a bit vague, as I didn't have time to really dive into it to make it repeatable.
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