First, PLCs allow us (as do programming languages for PCs) to treat data stored in memory (M-tags and DBs) ever how we like despite whatever we define tag datatypes (as basic, system data types or UDTs).

We can load a Siemens S7 String into a DB, point the MB TCP server to the 3rd byte (start of the character data of the string), and send it as simple ASCII data.

You failed to mention whether data is being sent to the client or received from the client.

The answer differs, despite being based on the same thoughts stated above.

Emre_Aslankara

Hi Mawton,

I am having the sam issue after 10 years from your post, I hope you will see tthe answer.

How did you solve it ? I am working  with a Modbus TCP client with S71200. There some Strings 24 bytes and you know plc outputs are QWords how am i going to writw 24 byte string into a word?

do I need to use conversion string to word? 

Thanks very much for your sharings

Emre