How to set tag value of date type?

[mglowinski93]

I've noticed that Date/Time tag type is returned by GetTagList as UDINT.

Can I somehow detect that it's a tag with Date/Time type?

How should i set a value of such a tag using pylogix?

[TheFern2]

I want to say that's just an epoch value. So convert your date time to epoch and then write to tag.

For figuring out if is a date/time value tag, I don't know if there's an attribute in the Tag class but you could check whether the value is epoch valid. i.e. if the value is up to date meaning within a month, you could check whether the epoch value is greater than N day. This could disqualify other udint values that aren't dates/times. Another way is to give proper tag names to datetime tags.

[dmroeder]

It appears that the documentation is from the Micro800 platform. You can choose a DATE type and a TIME type, both of which are 4 byte unsigned integers. When requesting the tag database, TIME and DATE types all report 0xc8 (UDINT). Neither appear to be unique data types, kind of strange.

[TheFern2]

yeah if is udint is hard to know unless it is using epoch then you can sorta validate, I would imagine it is, how else would time be calculated? If epoch is out of the question, I would just append all my tags with _time, and _date. However if plain epoch can fit in an unsigned type I would just use epoch instead and avoid all this mystery with this special types.

[mglowinski93]

I will try out this epoch solution. Once i check that out, i will let you know.

[TheFern2]

One thing to note is that to represent the entire epoch you need a floating type. I am not 100% positive if epoch fits in REAL, or LREAL. If epoch is larger than the max size of these types. Then you need to split secs and nsecs kind of like is done in the ROS framework Time class http://wiki.ros.org/roscpp/Overview/Time link for reference but you'll need a struct in the PLC with two int32 types. Also well epoch won't fit on 32bit systems by 2038 as that number is growing daily https://en.wikipedia.org/wiki/Year_2038_problem.

[kyle-github]

Most POSIX systems moved to 64-bit signed integers for epoch time in seconds. That's enough for a while :-) LINT on a AB PLC.

[dmroeder]

I'm unaware of a date/time tag type. There is display style of date/time for LINT types. Is this what you are referring to?

[mglowinski93]

Yes, exactly.

My intention is to detect, that variable should be displayed as date/time :)

[mglowinski93]

@TheFern2
Indeed, converting and parsing DATE value to epoch value did a job. Thanks a lot!

[TheFern2]

Nice! Glad to hear that!