Most efficient way to backup variables

PLCnext Engineer
1

Hello, I am fairly new to the whole PLC Next platform and PLC Next engineer, currently we are using version 2020.0 LTS. For my current project I have various variables (config settings and hour counters) which are configured as retain variables, during a powercycle all variables keep their values as intended. But during downloads everything is set to the initial values (obviously), because this is rather annoying for e.g. an hour counters I want to implement an automatic backup of some of the variables. Could you point me in the right direction how this can be done with this platform? I was thinking about one of the following options, but maybe you have other (better) options:

                                             1. Install and use 'Datalogger' app from app store 
                                                * <https://www.plcnextstore.com/#/169>
                                             2. Write variables to file at certain times and create an option to read the file back to the variables.

I do not need any historical values, just a way to restore the current settings. Thank you! Kind regards, Mike

2

Hello Mike,

there is no such functionality in the Datalogger library to my knowledge. I suggest saving the variables to a file and restoring data from that file on demand If the PLC starts with initial values.
The format to store the data is to your choice, a byte array might work fine but if you want it human readable maybe something like json would be a nice option.

I also suggest you store the File at the /tmp directory regularily and only move that file to the SD on demand to keep the writecycles to a minimum.
(You probably want to take Shutdown/Restart ect events as an indicator when to store data…) Some hints can be found here or here.

kind regards,
Oliver Warneke

3

Hi Oliver, Many thanks for your answer, at the moment I’m busy with another project, but I will try to implement this in my program as soon as possible. I will come back to you when it’s done or when I have further questions. Kind regards, Mike

4

Hi The newest firmware 2020.6.1. uses Extented Retain handeling, and works much better than the 2020.LTS. FW.

Try that one. Now it’s keeping the retain values in case of download. - Emil