Best practise for oneshots in tia

Holmux

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Hi

I never got around to finding a good system for oneshots in siemens.

In AB i would normally use a DINT and point at the bit, this way I can see what is in use and which are free.

What is the best way to handle this in a Siemens plc (Tia 15.1) ?

/Flemming
 
Dont know what you mean with "Use a DINT" and "point at the bit".

Oneshots and the resulting output are usually used within the block where they are programmed, so simply define BOOLs within the FBs declaration that you use for this purpose.
If I have a variable 'name', then I declare 'name_ons' for the oneshot, and 'name_imp' for the resulting output.
 
Holmux said:
Hi

I never got around to finding a good system for oneshots in siemens.

In AB i would normally use a DINT and point at the bit, this way I can see what is in use and which are free.

What is the best way to handle this in a Siemens plc (Tia 15.1) ?

/Flemming
Click to expand...

Yes same, much easier.

For TIA, I just use the tag name followed by _ONS and create a tag table which houses them all.
 
JesperMP said:
Dont know what you mean with "Use a DINT" and "point at the bit".

Oneshots and the resulting output are usually used within the block where they are programmed, so simply define BOOLs within the FBs declaration that you use for this purpose.
If I have a variable 'name', then I declare 'name_ons' for the oneshot, and 'name_imp' for the resulting output.
Click to expand...

I think he means he declares a DINT with name ONESHOTS, then uses ONESHOT.0 to ONESHOT.31 as his ONS bits.
 
Hi all

Thanks for your input

I was "hoping" there was something I overlooked, it is just nice to be able to see which oneshots are in use when you need to pick one :)

I will get the hang of the Siemens way

Thanks
 
JesperMP said:
Dont know what you mean with "Use a DINT" and "point at the bit".

Oneshots and the resulting output are usually used within the block where they are programmed, so simply define BOOLs within the FBs declaration that you use for this purpose.
If I have a variable 'name', then I declare 'name_ons' for the oneshot, and 'name_imp' for the resulting output.
Click to expand...


I basically do the same thing as Jesper, it's always made sense to me.



I also want to recommend that a big part of the best practice is using tags local to an FB as much as possible. ONS bits would need to be STATIC, not TEMP, tags.


If you really want to do things the AB way, you could use an array of bools, instead of a dint, but I wouldn't recommend it.
 
Holmux said:
Hi all

Thanks for your input

I was "hoping" there was something I overlooked, it is just nice to be able to see which oneshots are in use when you need to pick one :)

I will get the hang of the Siemens way

Thanks
Click to expand...


To be clear: the advantage of using the suffix naming is you don't have to track which ones are in use, because they are all separate. There's not really much advantage to try to lump them all together, at least in Siemensland.


If you are so close on memory you need you need to pack your oneshots to save space, I think you'd probably save money by buying a bigger processor than spending the engineering hours trying to optimize things.
 
mk42 said:
I also want to recommend that a big part of the best practice is using tags local to an FB as much as possible. ONS bits would need to be STATIC, not TEMP, tags.
Click to expand...

This is one of my gray areas in Siemens, I never really spend much time working on local tags, I would greate different tag lists or DB's, but all global.

It is on my bucket list :)
 
Last edited:
One tip is to set aside a bucketload of BOOLs so that you can add another oneshot at runtime without having to reload the either the shared DB or the instance-DB.

You will then have symbolic names such as #spare_ons_01, #spare_ons_02, .., #spare_imp_01, #spare_imp_02, .. etc. rather than meaningful symbolic names.
But it is worth setting aside some spare memory for online changes without having to change the declared data.
Also, memory is plentiful. 15-20 years ago one would constantly think about conserving memory. Nowadays one must think about writing code that is easy to understand and maintain.
 
I just make an array of bools to use.

You can point to bits in a DINT in TIA if you wish to keep a "standard" across platforms, up to you. Many ways to skin a cat
 
Holmux said:
This is one of my gray areas in Siemens, I never really spend much time working on local tags, I would greate different tag lists or DB's, but all global.

It is on my bucket list :)
Click to expand...

Local variables are fun and cleaner than global DBs. Less to keep track of. Fairly simple to learn. Temp variables exist only in the current block, Statics are stored between scans.

Looks like all the considerations have been covered by other posters.

For the sake of good habits, refer to the software as 'Portal' in shorthand, please don't call it 'TIA'.
 
Last edited:

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