S7-1516 MB_Client (best approach)

Hi there,

I am using an S7-1516 cpu and need to create multiple instances of mb_client to read data from three modbus servers. I am running TIA pro V15.

Each server is basically an ethernet bridge with a serial connection (RS422/485) on the other side. Each bridge will have a unique IP address and the serial connection will be 19,200 8N1.

The max block read of the modbus slave (downsteam of the bridge) is 64 words. I need to read at least 6 blocks of 64 words of data. Most of the data is in holding registers, but there are some coils as well.

Each slave will have a default unit ID of 1. I presume this is ok because the ethernet bridges are independent? It's changeable anyway.

Can anyone advise my best approach here in terms of implementing the MB_Client block?

Can I use just one mb_clinet per server (ethernet bridge) and dynamically change the modbus addressing and pointer to where the data is stored? Or should I use multiple mb_clients for each modbus block read?

If I can use just one mb_client per server, can they operate in parallel? Do I need to change port numbers in this scenario?

What is the limit on the number of instances of mb_client I can use with an S7-1516 cpu?. The Siemens technical data isn't specific.

Which version of MB_Client is best suited to my application? I can choose from V3.1, V4.1 & V5.1

Any advice on best approach here would be appreciated.

Regards,



Justin

No experience with Modbus.

Maybe this helps regarding the number of modbus clients:
Which ports are released for Modbus/TCP communication and how many Modbus clients can communicate with a SIMATIC S7 PN-CPU as Modbus server?

I'm not 100% familiar with the MB blocks, but you almost certainly want to use the newest version of the instruction available to you.


My understanding is that the MB TCP blocks use the TSEND instructions internally, so whatever TSEND limits apply to your CPU is what matches up there.


Big picture, though, it probably makes sense to use one MB_Client block call for each MB Server, and then dynamically change the addressing and pointer. It's possible there could be a weird reaction if you have multiple simultaneous requests from the same client to the same server. In my experience, MB & MB TCP devices are the most likely to have minimal/bad network implementations.

As long as it is Modbus TCP, You can call multiple instances at once, but You have to assign each instance a different connection parameters and unique connection ID (Conn_OUC).

Haven't used 1500 for modbus, but connection resources for modbus depends of 1500 CPU type.
Communication manual have table on page 270. Possible communication is between 54-182 if no other communications and if I understanded table right. (1516 have 236 resources)



https://support.industry.siemens.co...-200al-et-200pro-communication?dti=0&lc=en-WW


Since resources is much more than on 1200 and 300 CPU's, I would program each query separatly with own MB client block.



Also if you program blocks dynamically, it would mean that you can only make only one query at time even on TCP side?


MB block version depends of CPU firmaware and TIA portal version. If you have older firmware on CPU than blocks version, then newer blocks probably won't work.


For older versions, there is info (1200 CPU, but modbus blocks are same)



https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjhqO_Exv3hAhWdxcQBHfbKCbMQFjAAegQIARAC&url=http%3A%2F%2Fwww1.siemens.cz%2Fad%2Fcurrent%2Fcontent%2Fdata_files%2Fautomatizacni_systemy%2Fmikrosystemy%2Fsimatic_s71200%2Fmanual_s7-1200_2015-01_en.pdf&usg=AOvVaw0nOXwxxSJRYawTaekEYYfQ