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Asked:20 Oct 2025

Communication / Networks: mb_server 8383

Hi.
I have a problem with the mb_server block in TIA-portal. Attached there is a screenshot of my program. See references in bracket
I have two PLC’s, one with a mb_server block [2] and another with the mb_client [1] block. My goal is use the client block for writing data to the server.
When I use mode 0, to read data from the server, I can see that the value in the buffer of the server get transferred to the buffer of the client [8]. For some strange reason when I change to mode 2 [3] [4] for writing data to the server I get the error code 16#8383. [6] I have exactly the same setup, e.g. mb_data_addr, mb_data_len, etc. [7], so to me this is a mystery!
16#8383: “Error reading or writing data or access outside the address area of MB_DATA_PTR. The error can occur locally as well as with the instruction "MB_SERVER".
I tried use a modbus program on my PC, but I get the same result. Function code 3 (read) works, but when I use function code 16 (write), I get the same error.
My hardware: CPU 1212C AC/DC/RLY (client) and CPU 1212C DC/DC/DC (server).
TIA-portal: v13 sp1 upd9.
I tried updated the firmware to 4.2.0 on both PLC’s, but I get the same error.
Help is highly appreciated.

#sosflex #Communication / Networks #siemens
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Answers(1)
Siemens Test Added an Answer on20 Oct 2025

Modbus Communication Error in TIA Portal V13 SP1 UPD9

Siemens Self Support here, integrated with SiePortal. The error code 16#8383 ("Error reading or writing data...") with the MB_SERVER/MB_CLIENT blocks usually indicates an issue with the data access or address range during a write operation.

Here's a breakdown of potential causes and troubleshooting steps, based on your description:

  • Address Range Validation: Double-check that the MB_DATA_ADDR and MB_DATA_LEN parameters are correctly configured in both the client and server blocks. Ensure the written address and length do not exceed the allocated memory area for Modbus.
  • Data Type Compatibility: Verify that the data type you are attempting to write is compatible with the server's data type at the specified address.
  • Firmware/Software: While you updated to v4.2.0, confirm compatibility between the TIA Portal version (v13 SP1 UPD9) and the PLC firmware. Sometimes, older combinations can have unforeseen issues.
  • PC Modbus Tool: The fact that a PC Modbus tool also fails with function code 16 points to a configuration problem *within* the PLC Modbus setup, not a TIA Portal issue.
  • Permissions/Access Rights: Ensure that the Modbus server is configured to allow write access from the client.

SiePortal Resources:

If the issue persists, provide the exact configuration details (screenshots of the MB_SERVER and MB_CLIENT block parameters, especially address and length settings) for further analysis.

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