Default Status of Variables

What is the correct procedure setting the default value of Boolean variable?

What I mean is if you have several inputs that can be in either True/False state, how would you set these variables for the FIRST SCAN?

Thanks

That probably depends a lot on what hardware you are using.

In general practice, you should never use a variable while it has an undetermined value. It is often a good idea to set everything to zero on the first scan, however, specific variables may need to be true, depending on your program logic.

If you can, don't start your sequence or your real logic until you can confirm that your inputs are active.

That's a wide open question. It's a bit like asking "what pressure should my tyre be?"

Is it a car, truck, bicycle, forklift, childrens scooter, or a pallet jack?

Are you using it on concrete, bitumen, sand, grass, dirt, or in the swimming pool?

Are you racing on it, carrying a heavy load, floating down the river with it around your waist, or putting it in the boot as a spare (or in the trunk for all you americans )?

The question is meaningless without context.

damica1 said:

... if you have several inputs that can be in either True/False state, how would you set these variables for the FIRST SCAN?

Click to expand...

I don't think you need to worry about it.
If your system powers up and you have a power on delay, all your I/O will be scanned and your inputs will be updated.

If it's a non-CompactLogix or non-ControlLogix then the I/O update occurs before the logic scan anyway.

Or maybe you're not talking about AB PLC?

Thanks danatomega