Hello ! I am sorry that this type of question has been asked many times, I have trawled through the forums and not found exactly what I am looking for.... I have an S71214 on a network with 18 checkweighers. I am trying to use MB_CLIENT to pull data from them. 

I can connect successfully and get data from 1 device. I have tried cyclically polling each device and storing their data into separate DBs. I started off trying to use separate instances of MB_Client but ran out of working memory, and have now learned that I could only have a max of 8 instances apparently.

So I am trying to use just one instance of MB_Client, and once each connection is established, completed etc I try to DISCONNECT that connection and stop scanning the code of that instance, then scan a new block (using same instance of MB_CLient) but with NEW IPV4 connection parameters.

HOWEVER, it seems that MB_Client will not "let go" of the connection parameters given to it the first time it ran... It looks like even though I "think" I have disconnected and reconnected it still grabs data from the previous device. I have tried using the instance DB associated to MB_Client and monitor its STATE and CONNECTED and ACTIVE conditions - but am struggling. I was wondering if anyone can give further advice or better still give a small sample of code that could help me please ? Many thanks. Steve

1. Firmware version of the CPU
2. Software version used
3. Version of the Modbus TCP instruction used
4. Some screen captures or sample program

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Hello and thank you for the response.

The CPU is a 1214 DC/DC/DC - 6ES7 214-1AG40-0XB0  Firmware rev 4.3

The instruction I am using is MB_Client (modbus TCP) ver 5.1

Attached should be a screenshot of the actual MB_CLient instruction. I am using the "DONE" or "ERROR" tags of the instruction to then subsequently call for 10 different information from the same server. (In a "cylic" cascade running through each of the 10 calls one after another - but that is ALL to the same server)

Once I have called 10 times and DONE_10 or ERROR_10 goes TRUE then I try to disconnect by setting TRUE the DISCONNECT tag, and increment a cyclic counter. In OB1... as the cyclic counter increments it calls a new function containing the same instance of MB_CLIENT (DB22) but with NEW "CONNECT" parameters hoping to establish a NEW connection to a different server and go through the same process of polling 10 different pieces of data.

Sorry I dont have more detailed attachment at the moment. Ultimately I am looking around to see if someone has been able to connect to more than 8 devices using MB_Client...

Many thanks,

Hello.

There are projects of mine that uses Modbus/TCP.. but it is to only one peer. In quick inspection the descriptions you give seems all okay. I am not sure how you sequence the switch-over from one device to another. That is something of importance when I used Modbus RTU for many slaves.

I have found for you a sample project that uses a sequencer to switch between two devices. Have a look at what is done there. I have looked at the V14 one which is coded in SCL. The V12 one might be coded in LAD.

Data Communication between S7-1200 and SENTRON PAC3200 via MODBUS TCP (Set 22)

Late note..
You could consider the wrapper made available here: 
Extended Modbus library for Siemens PLC's

I have used the Modbus RTU portion which worked brilliantly.

~

THank you for taking the time to reply....

I have downloaded the examples will take some time reading through and testing to see if it works for me, or if and how I could adapt the code to suit. 

Many thanks,

Hello,

hope you find something next to qwazee's perfect help. I see your topic name so I think probably about your already used connections, not free for other connections. In this case is possible in connect instance DB change parameters for what you need, each time you need to have all tasks closed/finished and then disconnect from Server (parameter to set true and check), REQ false is then enough.prior change any parameters like IP or Port of new server required for poll. You can do this cfg for never ending number of Servers, if we can say like that. You can have one Server task in progress but other connection after that steps you can change and set to other Server and again as was described.