The 8 Results of 2 Digital Input Commands

[RMA]

But They are !

And i honestly believe that seimens are trying to take over the world! Buts thats another subject

Well, I certainly wouldn't try and claim that Siemens make your life easy, but I do find that some enthusiasts for other manufacturers swear that their favourite system is so intuitive a 12 year old would get on fine with it. Sorry, I don't buy it, this is just the usual "what I'm used to/have worked with for "n" years is easy".

Actually, as a fugitive from the DCS world, my biggest problem is the cylical "Ablauf" - can't find a suitable English expression - process, operation, running system? I'm sure this problem will plague me regardless which PLC I'm using.

I'm not an electrician, I'm a Process Control Engineer. I'm happiest programming in SFC where I can take my Flow-Chart and translate it 1 : 1 into an SFC program. Translating a Flow-Chart directly into the cyclical Ladder, Function Block or even STL is an impossibility! I've never programmed using States, but I suspect I would get on with that OK as well.

If I can't use SFC, then as a previous H/W designer, I find Function Block most comfortable - reminds me of IC logic design, same applies to Siemens CFCs, the only time I use ladder is when Function Block produces something which covers about three screens and Viewing is easier in Ladder, which is usually a bit more compact. As far as STL goes, I get on quite well with that, perhaps as a result of many years programming PDP11s in machine code, however, that gets difficult as soon as Edges or Timers get involved!

I get the impression that the majority of the members here are electricians, at least by background, which probably explains a preference for ladder.

As far as logic goes I prefer TRUE and FALSE and I can't say I have ever seen anywhere in the Siemens documentation where they use NC / NO, there again the Siemens documentation is so extensive that I doubt I've read more than 5% of it!

RMA,

I checked my Siemens ladder, and it calls them "Normally Open" and "Normally Closed". The NO is okay, but the NC is a misnomer, a paradox.

Maybe it's because I'm using the German version but mine are calle TRUE and FALSE - yes, in English!

RMA,

Is Siemens still using the old TI mnemonics? I programmed a 5TI back in the day and seem to remember a Load, Load Not, or an LD, LD Not to examine the input status. Did not take a lot to get from there to XIC XIO

I've never used the 200 series, but I believe the S5 series also used to use the LD command for the first entry in a boolean logical structure in STL. With S7 that is no longer the case, boolean structures are described purely in boolean terms. In other words:

A M0.0
A M0.1
O M0.2
= Q0.0