Hi all,

We have 10 S5-95U PLCs. We want to communicate with all of these PLCs and collect some data from a S7-400 station. Some of these S5 PLCs don't have a profibus port and some of them have an OP on PG port. So we don't have a chance to make a profibus network. I think the best solution is communication via serial interface (CP521, ASCII free
protocol). Of course, we don't want to buy 10 serial CP for S7-400 station. For this, I thought to use a Serial/Ehernet converter and buy a ethernet CP for S7-400 station. Any idea? Thanks.

 

The CP521 is fairly slow if you have more than a few bytes of data. The "frame" method of data transfer will take multiple scan cycles to complete one transfer. This means the PLC backplane will be a serious bottleneck for larger amounts of data. I have looked into a very similar scenario with the S5-95U, and there are very few if any good solutions.

Read the CP521 manuals for details on how this bus cycle works. I have used the CP521 Basic but not the CP521 SI (the first has a Basic interpreter, while the second is a serial port with add-on protocols). If the SI is similar to the Basic, then you can probably transfer half a dozen bytes in each scan.

If you intend to take the data back to a PC at some point in this system, there are a number of serial to ethernet converters which you could connect to the PC and bypass the S7-400. I looked at one by Digi which you might consider. It supports the 3964/3964R protocol, which I believe is a native protocol for the CP521 SI as well. Using a standard protocol may require less programming work than free ASCII.

I am not familiar with any ethernet attached serial converters for connecting to an S7-400 but there are a number of Profibus-DP slave to serial converters on the market. You may wish to look into whether any of them support 3964 and whether using this will make the data transfer between the S5-95U and the S7-400 any easier or more reliable.

If you need to collect just a few bits of data (e.g. auto / manual / fault / etc.), consider using digital I/O from the 95U to blocks of Profibus-DP slave I/O modules (i.e. - the blocks are I/O slaves for the S7-400). You can do combinatorial logic on the status bits back at the S7-400 to calculate things like down time, cycle time, etc. If you are trying to access several integer numbers however, this is less practical.

If you have a large amount of data and need fast update times, the Profibus port on the S5-95U may be your best (or only) option. If you decide to pursue this further however, be sure to check what type of Profibus port is installed in each CPU. There were three Profibus models in the 95U line - Profibus-DP slave, Profibus-DP master, and just "Profibus". The last one in this list is a version which was intended for peer to peer communication, and uses a different (obsolete) form of the protocol than DP.

 

Hi,

How much information do you need to transfer and how often?
--
Marc Sinclair
http://www.germainesystems.co.uk

 

CP521 is kind of beast I never liked much, some months ago (after so many years) I had to install again one of these nasty things and yet I hadn't any fun. If you have any chance, use CP521 BASIC instead. Be aware that CP521 (as all "intelligent" modules on S5-100U bus) can be mounted within the first 8 modules range only, so you must check your PLCs configuration and, in case, you may need to move existing I/O modules and rewire the PLC program accordingly. If your budget is limited and if you have not much data to exchange, I would evaluate the option of a slow but cheap communication via digital I/O lines (e.g. data+clock+synch = 3 inputs and 3 outputs on each partner). Use optocouplers in between.

Just my opinion

regards
Luca Gallina