Hello, I am having a similar problem. I am trying to read one register from a modbus server installed on a PC (linux),  with a S7-1200 over Modbus TCP using MB_Client. But i'm not able to receive any data through modbus client function.

The error bit is activating with a frequency of 5-6 seconds and Status Value Is changing periodically between "16#7005", "16#7006", "16#8383". Please see the attached screenshots.

What can be wrong?

Modbus Server (slave)  has IP 192.168.50.1 and ID 3
The register I am trying to read has adress 2 (40002)  (word 16 bits) (Value forced in modbus server = 6 (dec)).

I tried to read the register 40002 with modbus scanner application (CAS) running on PC and I received correct value.

Thank you and

Best Regards

Hello,

one idea, look to your STATUS values in TIA help with MB_CLIENT instruction. All describes that conection is established, data was sent and received but probably your DATA address request is wrong in parameter MB_DATA_PTR. Simply for first, do you have enough place defined if you want 16 Words? Second, try in pointer use for test only pointer notation like P#..... WORD 1. Does something change?

Hello, tahnks for your answer Duris_I,I've already looked into TIA help , of course the status values "16 # 7005",and "16 # 7006" seem to be okay according to description, except 16#8383, but i still receive no value in MB data Block and DONE output of MB client function never becomes true.

Regarding the DATA address request, I also tried several variants: eg.

1. MB_DATA_ADDR = 40003 and MB_DATA_LEN = 1

2. MB_DATA_ADDR = 40002 and MB_DATA_LEN = 2

3. MB_DATA_ADDR = 40001 and MB_DATA_LEN = 2

4. MB_DATA_ADDR = 40001 and MB_DATA_LEN = 4

5. MB_DATA_ADDR = 400002 and MB_DATA_LEN = 2

6. MB_DATA_ADDR = 400003 and MB_DATA_LEN = 1

and other….

Regarding the space in the data area, I think it is enough because I've defined an array of 0-16 words. See attached screenshot.

I also tried P#..... WORD 1 and nothing change.

If you have any other idea, please be kind and let me know.

Many Thanks

Hello,

I see problem probably on PC side with definition available register and data for PLC requested area. I don't know that app on Linux. Maybe you can attach screen what you have defined available on that PC SW as Server, what register and data defined because if you request from PLC with your cfg, probably no problem. What you have defined also as request if you make local connection with 2 app as Clien and also as Server?

I have the same problem, but now solved.

https://support.industry.siemens.com/tf/ww/en/posts/modbus-tcp-ip-s7-1200-not-connect-to-partner/178639/?page=0&pageSize=10#post713457