Add page describing special variables (e.g time)

[garretfick]

There are a number of useful variables that can be accessed, but are undocumented. Document them.

[DrEagleTalon]

Are there any on this page, https://www.openplcproject.com/reference/ that you would prefer be done first, and what would you like the Markdown to look like? Follow any kind of Template? Would you like a Template made? Or just follow the other Reference Pages for Template?

[garretfick]

Thanks for the interest in contributing here. My thoughts:

1. Don't repeat yourself - that means use templates to create a common format (it helps the reader).
2. It would be great to have a standard format the specifies the names and types of inputs and outputs.
3. Avoid diagrams that don't have accompanying text (bad for search and for various visibility abilities). Most (or all) pages violate this today.

For the second item, I imagine something like:

FUNCTION_BLOCK PUBLIC FB_Machine
VAR_INPUT
  bButton       : BOOL;
  bInsertCoin   : BOOL;
  bTakeProduct  : BOOL;
  bTakeCoin     : BOOL;
END_VAR
VAR_OUTPUT
  eState        : E_States;
  nProducts     : UINT;
END_VAR

I don't have a preference for what's first. Everything would be an improvement.

I'd be happy to review an early template.

[DrEagleTalon]

@christinezaytsev I see you contributed a lot of descriptions yourself. any you left off on or any help you can provide would be great! Looking forward to helping as much as possible.

[garretfick]

I'm working on a template to help give a common way to structure the page.

If you are going to undertake a significant amount of work in this area, I see cppreference.com as a good model that I would like to emulate.

[DrEagleTalon]

I do plan on doing a lot. I won't be starting right away since I am working on a new project at work, but once I'm through the initial crunch, I am going to get as many done as possible. Furthermore, I had a template in mind but hadn't put it in writing yet, and cppreference did a good job of it. Maybe what they have with some readability to it as well.