Hi All,

I am using S71200 CPU to use the controller for MODBUS TCP-IP communication application where client will be communicating with the controller with Modbus TCP/IP.

Software using TIA-v18, CPU: S7-1212C, IP Address (CPU): 10.175.178.233  ;  IP Address (MB_Client): 10.175.178.47 ;  Subnet: 255.255.255.0  ;  Port: 502

Initailly whicle development I used and tested the program with IP address staring from 192.168.1.*** series it worked fine, when I am in customer site customer requested in change in IP address series as mentioned above, hence I only chnaged the IP address within the Datablock and tried to check but I am unable to establish communication within CPU and the modbus simulator software as well. my main objective is to Write to the modbus registers. hence i have used only one MB_Client block with MB_mode =1.

And even customer are unable to see on there end. I am confused the program is same with only the IP address differs, but now nothing is working even I cant able establish comms with 192. series.

can anyone help me with this issue please.

Regards

Hello,

Do you know correctly what Subnet is used, you write 255.255.255.0, I opened in google IP subnet calculator it writes must be 255.255.254.0

If this not help have you tried again rebuild hardware and software and then download project to PLC?

Hi,

Updates about the issue.

The subnet mask which customer is using in there plant network will be 255.255.255.0, hence I need to be in the same subnet as well. And they have a gateway address of 10.175.178.1, which I have assigned in the program as well (in Default router access).

So PLC have IP Address of 10.175.178.233 ; Subnet: 255.255.255.0 ; Default Router (gateway): 10.175.178.1 ; Modbus TCP/IP (MB_Client) : 10.175.178.46

Strange thing is currently i came back from site and tested with the other controller which I have with me now, I can see program is working and I can see the data transfer via 'Modbus Slave' software.

I have sent the same program to my Engineer who is in site who have the same TIA v18 and Modbus slave software installed in his laptop and able to load the program backup to the controller successfully which is in site, but I cant prove its working via 'Modbus slave' software and neither the customer is able to pick up the controller via Modbus TCP/IP on there end.

Dont know where is the problem, I completely reset the controller and loaded the backup but still no luck.

Can anyone explain how to overcome this issue please.?

It is really strange on this issue.

Regards,

Hello,

sry, little bit chaos that I see. I don't see still what Server device you are connected to. I see also some network not correct settings probably. If you want test correct functionality at site, you need have your PC network set up like PLC expect, IP and SMask with router possible if it needs. Then try test data exchange via suitable PC MB TCP Client application to Server. You mentioned previously, your test was ok but who knows what you have defined at your PC at that time. Simply, you need say all cfg correctly at all devices you have because then it is only chaos and no help can be provided. Try take to account olso one thing as important, with PLC working as Client, your Server device has also possible formal RTU address defined probably so if you don't set up this also in PLC (MB_Unit_ID), it can be possible that you can connect to Server but no data you will have.

Hi Duris,

Thanks for your reply, at client place they have a centralised SCADA (Schneider) which will be communicated via Modbus TCP/IP with Siemens controller installed.

After struggling with (MB_Client) I uderstand and noticed that it will be better use MB_Server as per the current configuration which client have on there end for communication. Hence modified the program to have MB_Server instead of MB_Client with the same IP Address and Gateway, which finally defines the Siemens controller has Slave devices within Clients Network.

Its been tested with Modscan (Lab & Site) and also working fine with Clients end as well

But still cant understand what was happened with MB_Client program version which I tried earlier (Just forget about the communication with Clients SCADA, I couldnt able to prove that the controller is communicating via Modbus TCP/IP within our laptop using Modbus Slave software).

As I said earlier I have used same program (with MB-Client) but with different laptops I know what might need to be confogured on laptop end to communicate, but it was working with my Laptop/PC, but not in clients side or our service engineer PC, its still a mystery for me.?

Regards,

hi, i am also facing the same issue, have you solved the issue???