Test your S7 Knowledge

[L D[AR2P#0.0]]

9: "When is the PII updated?"
Answer a: "Prior to execution of OB1"
Answer c: "At the end of execution of OB1"
Obviously the whole sequence runs around in cycles. I have also seen some official statements that the cycle is OB1 - PIQ - PII - OB1 etc.

Answer c is correct as you have shown the sequence from start-up.

 

[rsdoran]

Those were my wrong answers (guesses) but what the heck.

Maybe a good reason to refrain from participating in this topic.....?

Why not participate? I may not be experienced per se but have worked with them, will not learn more unless I am willing to participate. The only differences (overall) between brands are specifics like how the addressing is done or differences in how the instructions work.

When it comes down to it I am not proficient at programming any plc and may not know specific details about any particular brand, that said what I do not know I can find out.

Since the request was made.

 

[JesperMP]

Answer c is correct as you have shown the sequence from start-up.

With that question and the 3 others, I had to guess what answer the questioner wanted to have rather than what is the most correct answer. So I answered "a" and got a correct answer in my score.

 

[S7Guy]

Yes, the PI is updatted before OB1. Years ago, it was at the end of OB1, but around 1998 or so Siemens determined there could be possible safety concerns on a restart (the outputs could go high for one scan) so the processor was changed to update it before OB1 starts. Of course, once it starts cycling it doesn't make much difference.

 

[geniusintraining]

Maybe a good reason to refrain from participating in this topic.....?

Pego,

What did you add to this thread by your post? Let me answer for you, nothing!,

Ron replied because I ask him too, he is a smart man and I enjoy reading his post.

Maybe we all should just read and nobody post and everyone keep their thoughts to themselves.

This would be a great site then...we could just all see who is logged in then we can go

 

[RMA]

I would have had 100% but got caught out on the BCD question by trying to be too clever and changed my original answer of 291 to take account of byte order had the data been stored in a DW - which was not explicitly stated.

 

[Jeebs]

92%

got me on the PIW on S7-300 and the Global DB.

-Inputs are read before OB1, outputs (re)set after OB1.(thats how it was explained to me)
Viewing it from another point: Are the inputs read after OB10x and are outputs set after OB10x? Cause we all know (well most of us) that OB10x will run first on start-up and the sequence starts immediatly after. (OB10x being either OB100, OB101 or OB102)
-Almost every S7 has a MPI port (haven't found one without) and as Jesper stated SOME have MPI/DP. Logically you would say the primary (as in most used) would be the MPI-port.

Jeebs

 

[aikona]

For some more tests try the following siemens link

 

[S7Guy]

-Inputs are read before OB1, outputs (re)set after OB1.(thats how it was explained to me)
Viewing it from another point: Are the inputs read after OB10x and are outputs set after OB10x? Cause we all know (well most of us) that OB10x will run first on start-up and the sequence starts immediatly after. (OB10x being either OB100, OB101 or OB102)

Yes, the process image is written and read after the start-up OBs are executed, but before OB1 is started. If you look up "Process Image" in help from Simatic manager, they bdescribe exactly what happenes. As I thought, they made the change in Oct 1998.

 

[aikona]

About OB1 and PI/PQ ... On the new S7-400 PLC's the PI gets scanned first then OB1 ( and all other interupts) then at the end of OB1 the PQ gets processed then some other internal stuff like comms etc.and then back to PI,OB1 etc

Eric