Seimens hidden Address..?

Matchu04

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While at work today I stumbled across somthing that I cant seem to get my head around. Basically there is a analog input / output card on a machine that I curious to see what they did. So on my lunch break I tried to identify them but got stuck.

I understand you can have different types of indirect addressing but I dont think this address as called as such (I maybe wrong).

So basically in my hardware config you can see the AI/O card with its address. Take PIW 20 for example. I can see in the assignment window that it is used but indirectly but should I not be able to access it via go to??

Pretty much the same but reverse for the outs. I cant see out word in the assignment but sure can see it when I go to.

I know its definatley me and my understanding of it but someone please help me...

Addressing Help.jpg
 
JRW said:
Is it address in the program as IW20 or PIW20?
Click to expand...

Both...

The output addresses are access like this e.g PQW 20 so when I went to go location PIW 20 it shows the location in the "go to window". But as you highlighted these are the peripheral imagew so wont show up in the assignment window.

The inputs on the other hand are used within the program as the process image e.g. IW 20 so wont show up if im searching it as a periferal but instead show up on the assignemnt window..

I was under the impression that analog I/O was always written/read via a peripheral address but this has proved me wrong..

Thank you once again guys...
 
They are IW20 / QW as the IO addresses have been remapped from the default locations to be back in the IO image area.
 
In the S7-300 the address of the IO modules is by default set by the slot the module is in.

Digital IO begins at byte 0 for slot 0 and 4 bytes are reserved per slot. Analog IO begins at byte 256, and 16 bytes are reserved per slot.

The default size of the process input / output image is 256 bytes.
Byte / Word / Dword references below the default may be addressed as IB / IW / ID

Addresses above 256 must be addressed with a "P" PIW 256

This system default can be overridden.

Your analog IO module is in slot 9
The default IO address range for an analog in slot 9 is byte 336-343
However in your screen capture the address is shown as 20-27 for inputs and 20-23 for outputs. So the inputs would be IW20, IW 22, IW24 and IW26. The outputs QW 20 and QW 22.

The size of the process input/output can be changed on newer processors - check the Cycle / Clock Memory tab of the CPU properties:
 
Maybe only '20' is passed to the input/scaling function that builds an address pointer of it.

In this case you could print the complete program to a PDF and search for '20'. Or unspecified 'IW'/'PIW'

Kalle
 
From the information in post #1, one can conclude this:
The analogue inputs are accessed normally and without indirect addressing, as IW20 and IW22 (not PIW20 or PIW22).
The analogue output is accessed as direct peripherial access and without indirect addressing, as PQW20.
 
The Input process image is updated from the actual Inputs before each execution of OB1 and the output process image updates the actual outputs at the completion of OB1. Understanding this can help to understand some programming techniques. EG witing to the same output multiple times - only the last one executed has any effect on the actual output.

The consequences of placing analogue I/O in the process image and accessing them within the process image is that the I/O will only update at the execution speed of OB1. This might be good for some applications but would be no use for a PID loop.

It should also be said that you can read digital I/O directly from the peripheral image too as in L PIB 100. This can be used to determine the actual state of I/O in an interrupt event as an example.

Nick
 
JesperMP said:
From the information in post #1, one can conclude this:
The analogue inputs are accessed normally and without indirect addressing, as IW20 and IW22 (not PIW20 or PIW22).
The analogue output is accessed as direct peripherial access and without indirect addressing, as PQW20.
Click to expand...

This is not always the case though??
 
Matchu04 said:
This is not always the case though??
Click to expand...
Not allways, but for the program you posted about yes. (edited, because it could be misunderstood).

What the others have written about default addresses and assigning addresses inside or outside the process image is also correct, but may have confused you more than helped you (no offense meant).
 
Last edited:

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