Tia Portal V19 | S7 1500 Series PLC

As a learning exercise, I've created a program in LAD and SCL that calls timers from inside a global DB from the main OB.

So in SCL my program looks as below, while my ladder program is attached.

"Motor".start.TON( IN := "Motor".startEN, PT := "Motor".PT);

"Motor" is a global DB which contains an IEC_TIMER named "start". I then tried the following in STL:

CALL TON, "Motor".start (ect ...)

It tells me "the instance data block doesn't match the called FB" which I'm guessing means my data structure doesn't match. I know if I create a FC block with an In/Out variable and declare my timer inside it using the In/Out it will work as intended.

I also know good practice states that I should use function blocks to make my code easier to read, and ordinarily I would, but this project is incredibly simple because I'm still learning which is why wanted to call the timer directly from the Main OB.

I want to know why I can't do what I did in LAD and SCL in STL. To me, needing to create lots of instance DBs seems messy, and surely it would be better to have an array DB which only contains timers inside?

JimHalpert 

Hello frogree

I believe it is possible to configure the TON with a global DB inside the Main OB. You should check this video:TIA Portal: How to declare Timer Tag for IEC timer?

Can you upload a screenshot of the timer declaration?

Good luck! 🐸

 Hi JimHalpert,

Thanks for getting back to me.

I have two questions: firstly, could you explain why it's bad practice?

Secondly, I attached my timer declaration in STL for you as requested. I did what the video describes for my LAD implementation, nice to know I did it correctly. 🐸 Unfortunately I'm not sure where to go from here - I think I need a temp variable that points to the global DB somehow, but you can't have static tags in the main OB, or In/Out ones.

0_Einstein 

Are you aware STL runs slower on s7-1500 PLCs?

Why anyone would want to run in "assembly language" for a PLC when higher level more compact and succinct languages are available, it really baffles me.

I recommend using the language for each piece of logic that makes sense.

If it's a bunch of contacts and coils, LAD is fantastic.

If it's a bunch of math, SCL is great.

If it is a bunch of code that _only_ runs in SCL, then of course, use SCL.

If it is code that nobody understands no matter how flawlessly it is written, then pick a language you and everyone who will need to support it in the future understands.

In my work, that means mostly LAD, with SCL where it makes life simpler.

You absolutely can and should use global DBs for TONs in OBs, whether it is OB1, or OB123 or OB2000.

For FBs, you need to use multi-instance timer tags in the FB interface so every call to the FB gets its very own block of tags for the timer.

Read the S7-1200/S7-1500 Style and Programming Guidelines (available on this support site).  It describes all these things far better than I can.

 Hi 0_Einstein,

Thanks for your guidance. I didn't know that STL is slower, why is that - is it because of the compiler?

I would much prefer to use SCL or LAD, but this is a problem set by my mentor at work to aid in my learning and he wants versions in LAD, SCL and STL. I can use an instance DB no problem, or if the timer is called in the FB but I'd like to make the implementation consistent across languages.

I did read the programming guide, and "Using IEC timers and counters" in the help guide accessed via Tia Portal but to no luck. I've read all the documentation I can find too, which seems to imply I can do it. The problem is that the example in "Using IEC timers and counters" uses a static variable, declared as an IEC_TIMER within a FB (I assume you could pass a timer as an In/Out too). Mine is just an IEC_TIMER within a global data block which is passed directly as an input to the CALL of TON in the MAIN OB. The main OB doesn't have static variables, so I'm out of ideas!