Siemens Step 7 PQW and PIB help

[Blue Fox]

Hello all,

I'm hoping someone out there can help me. I have 2 plcs where I work which communicate with each other. In one of them it transfers a MW to a PQW, The other plc then reads this I assume as a PIW and transfers it to a MW (again I am assuming). I am trying to find one bit of the input word read by the receiving plc but cant find how to view what PIW the receiving plc is using or which MW (If it is) its writing it to. Is there somewhere I can view a list of the PIW's used, anyway of tracking down where this is written to.

Many thanks for any help you can give me.

 

[JesperMP]

I am assuming that the two PLCs are exchanging the IO data either by Profibus master-slave or Profinet as I-Devices. That is the only way that the data can be excanged as part of the Inputs and Outputs.

There are several ways that the receiving PLC can import Input data.

1. By load of PIB, PIW or PID. Highligt any address in the LAD/FBD/STL editor and hit CTRl-ALT-Q. Then specify the address you are intested in (for example PIW256). Be sure to have the selection "Overlapping access to memory areas". That should give you a list of all accesses to that address.

2. By SFC14 (for reading data) and SFC15 (for sending data). In the same dialog box mentioned above, type SFC14 or SFC15. That will give you a list of all calls of these blocks.

3. By indirect addressing. Unfortunately I dont know an easy way to locate addresses accessed by indirect addressing. You can trawl through all the code and look for direct addresses to AR1 and AR2. It will take some interpreting of the code to establish exactly what addresses are being accessed.

 

[Blue Fox]

Thanks for the reply, I think I have now found which PIW its reading into, PIW 160, however when i search for it it isn't listed as being used in any location unfortunatly so I'm struggling a bit.

 

[JesperMP]

Thanks for the reply, I think I have now found which PIW its reading into, PIW 160, however when i search for it it isn't listed as being used in any location unfortunatly so I'm struggling a bit.

PIW160 would be unusual, since that would be inside the regular process Image. Typically (but not always) the process image covers bytes 0-255. In that case you can read just the normal input address (IW160 instead of PIW160). Try to use CTRL-ALT-Q with IW160.

 

[Blue Fox]

Thanks for the reply again, I tried using IW160 but still doesnt recognise it, I found the PIW through the symbol table in the end so am assuming it is correct, is odd though as all other piw's used are 400+, I am assuming its indirect addressed somewhere?

 

[Blue Fox]

Ok I found it, I got lucky and began trawling through the program and found a transfer for it. The reason it wasnt coming up under a "goto" search was because the symbol table is wrong! according to the symbol table I was reading on PIW 160 and sending on PQW128, having now found it im reading on PIW 128 and sending on PQW 160 so someone has got them the wrong way round at some point! Thanks for your help though.

I do have one more question though although I have managed to find it this time and hopefully wont have a similar problem again, is there a way of tracking if one plc sends out a PQW which PIW its going to on another plc? Guess it must be somewhere? I've never set up a signal like this to another plc on siemens only messaging on slc500 or done it to other inverters where I set up a node number to link the PIW/PQW to on step 7. Or even a list of the PIW's and PQW's a plc is using would help.

 

[Blue Fox]

Just to add to above in my case one plc is sending out a PQW 700 and its being recived on PIW 128 on the other plc - how do I tie these to together to make finding the piw 128 a lot quicker next time?

 

[JesperMP]

I am assuming the two PLCs are connected via Profibus.

There are two most likely variants.

1. The two PLCs are setup as DP master-slave.
If you open the HW Configuration of both PLCs, then one (the master) has the other PLC assigned as a DP slave. The DP port on the other is set to "DP slave" mode. In the configuration of the DP slave in the master PLC and the DP port in the slave PLC, you can see the addressing.

2. The two PLCs are both DP masters, and there is a DP/DP Coupler in between the two PLCs.
If that is the case, you can see the amount of data being transferred and the addressing in the configuration of the DP/DP Coupler in the two projects.