Why couldn't I use address 116?

S7PP

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Sep 2010
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I'm doing Hardware configuration on Step 7, S-300, 315-2PN/DP. Insert couple of DI, DO AI and AO module. When I assign them address, I assigned AI1 with 100 to 115, then I tried to give 116 to AI2, but the system doesn't let me, only want me assign 128. I don't have any other module using address from 116 and I checked Address Overview, the 116 to 143 is a gap.

Why is that happening? So wired.
 
The 315 has a process image of 128 bytes. You are attempting to set the address of the second analogue card so that it straddles the process image and the peripheral area. The h/w config will not permit this.
 
Last edited:
OH, I see. I didn't realize that. Is that means that I have use PIB/PIW or PQW to access the I/O address above 128 bytes? Is it make the cycle time slower?

Thanks a lot L D.
 
It is recommended that analog signals are out of process image area. You should address all your analog starting from 128. Yes then you need to use PIW/PQW.
 
I would recommend the opposite. I would stretch Process Image to 2K In and Out and then all the I/O is scanned at the same time. You can still use PI/PQ commands for quick stuff. Easier to force and will execute more stable scan times.

This is what is done for PCS7 by default. A nice byproduct of this is it allows you to cluster addresses by area or racks.
Rack 1 I/Q 100~199, Rack 2 200~299, MCC's 500 etc

Nick

TurpoUrpo said:
It is recommended that analog signals are out of process image area. You should address all your analog starting from 128. Yes then you need to use PIW/PQW.
Click to expand...
 
OH really? I thought adccess PI/PQ is slower than directly access I/O, when you say "You can still use PI/PQ commands for quick stuff." doesn't mean it is quicker, right?

Well I guess it will be neat than use half half.

thanks a lot.
 
Check hardware manager. It's been a while but I think V2.7 (don't quote me on this) or better.

I'm not running Step 7 on this box and don't have my VM image with me but will check later.
 
I think he means the peripheral area. He might want to use PI/PQ for all the IOs.

Maybe it's better than use some of I/Q and some of PI/PQ, because the scan time is very different.
 
Nick you are right, 315PN/DP lets you adjust p image size, but i would still rather use analog in peripheral area. Its 300 series cpu afterall.
 
You will slow down CPU a little in the beginning by scanning all the I/O but then you will not be doing any immediate reads/writes in mid scan. Read/Writes to I/Q are like working in M area and the stuff gets updated to real world and back during service break at end of scan.

I have had good real world results with this. On large projects.

Nick
 

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