Confused by Set in S7-200

Hi all,

I'm converting an S7-200 program to S7-300 and found something confusing.

The SET in S7-200 has a number underneath it which the help says equals how many 'bits' are 'SET'.





This example seems to agree with that. It says that if the number of bits affected is '6' (for instance in Network 2) then the bits SET are Q0.2, Q0.3, Q0.4, Q0.5, Q0.6, Q0.7.

However... I've just found this code in my program....



What does the 'zero' underneath the bit mean?

According to the help file it shouldn't mean any bits are SET ?? But surely that can't be right?

Any ideas?

Thanks

Diameter157 said:

http://www.plctalk.net/qanda/showthread.php?t=43318

Click to expand...

Thanks for that.

I'm still a bit confused.

Nick B said:

This is allowed because the n can be a variable (example MB10).

0 does nothing.

Click to expand...

So does it just Set or Reset the 'bit' that is addressed or does it literally do *nothing* as though the instruction didn't exist?

Confusing :-(

The way I read the post I assume it literally does nothing.

But assuming can lead to mistakes. Maybe you could simulate it in microwin?

Unfortunately I don't have a way of simulating it.

I originally thought like you that it did nothing. However, after re-reading it, it could also mean that it just Sets/Resets the one bit (i.e. does exactly the same as putting a '1' under the bit) ?

If I don't get an answer in here forthcoming I'll resurrect the old thread and ask.

Thanks

edit: never mind the download link is dead
http://www.plctalk.net/qanda/showthread.php?t=26343

Diameter157 said:

edit: never mind the download link is dead
http://www.plctalk.net/qanda/showthread.php?t=26343

Click to expand...

OK, thanks Diameter

I am going by memory but I believe 0 does nothing and to make the set / resets work you need to use a 1.

So I assume there is some sort of internal loop / indirect addressing where you are specifying the number of 'loops'. So if 0 is entered no code is actually executed.

But I can't find any other documentation on this topic either.

Thanks Joltron. Just seems like a strange convention. Why write anything if that's the case??

Very odd