11/3/2021 3:11 PM | |
Joined: 3/28/2010 Last visit: 10/12/2024 Posts: 1067 Rating: (213) |
It appears that you are trying to use a TIA function to read AND write data values in the same packet/transaction using Modbus. That's probably not going to happen. 1. A Modbus server must receive a Modbus command packet that is properly formatted with a valid Modbus Function Code (FC). It does not appear to me that your tactics implement Modbus function codes (but I'm a Modbus guy, not a Siemens hardware/softare guy so maybe you did have Modbus function codes somewhere). A server can execute only one Modbus Function code at a time so if you try to combine two function codes in one packet/transaction it won't work. There is a Modbus Function Code 23 (0x17) Read/Write Multiple Registers that allows a Modbus client to write data values to a series of server registers and read data values from a series of different registers in the same server in a single transaction/packet. However, it is not common to find either a Modbus server or Modbus client that implements and executes Function code 23 (0x17). A thread on this forum from 2010 says that certain Siemens hardware/firmware does not include FC 23. https://support.industry.siemens.com/tf/ww/en/posts/cp341-modbus-master-function-code-23-17hex-read-write-4x-registers/44224/ I disagree with the statement that Siemens is at fault for not supporting the entire Modbus protocol because I'm not sure any vendor supports the entire Modbus protocol. The real problem is the slave/server that executes only FC 23, which is the exception in the Modbus marketplace. Support for FC03/03 and FC16 is almost universal, support for FC23 is uncommon. Unless Siemens has added support for FC 23 its hardware/firmware/licensing since 2010, you're likely limited to reading (FC 03 or FC 04) in one transaction, then writing in a separate transaction FC16 (0x10) and that assumes the server can execute FC 23. |
Last edited by: danw at: 11/03/2021 15:13:39 |
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