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sqlsql-serverplcsiemenstia-portal

PLC S7-1500 SQL-Connection - received data shifted by 1 byte --why?

i´ve been successfully using a S7 1500 PLC in combination with an SQL-Server for quiete some time now. I set everything up like mentioned here: S7SQL-Guide-Stackoverflow Today i tried to add a second parameter to my SQL-Query. So I made something like this:

select Number1,Number2 from MYTABLE WHERE Apple = red and Sky = blue

The S7 sends the telegram, and the SQL-Server replies. So far so good.

TokenColumnMetaData

I set up the size of TokenColumnMetaData accordingly to my wireshark record, compiled and send the updates to my PLC. Now the part which I don´t understand:

I am expecting to receive the value "12345" so again I used wireshark to see what I should expect: wireshark-data

So what I got is: 39 30 00 00, which is 12345 just the bytes are reversed -no problem so far, but when I check on S7-side, I see this: S7-Watchtable

My input is shifted by 1 Byte. How can I solve this? Unfortantely I don´t have deeper knowledge of the code provided by Siemens for this application.

Edit:

Screenshot of typeUseCaseSpecificTokenrow

typeUseCaseSpecificTokenrow

Solution

  • Sometimes weird memory stuff happens when the data type comprises an odd number of bytes.

    Siemens starts each element on an even memory address. So if Length is at address 0 and Data is at 2-5, then address 1 may be getting the first byte that is intended for Data

    Address Data Element
    00 04 Length 0
    01 39
    02 30 Data 0, byte 0
    03 00 Data 0, byte 1
    04 00 Data 0, byte 2
    05 08 Data 0, byte 3
    06 47 Length 1
    07 94
    08 03 Data 1, byte 0
    09 00 Data 1, byte 1
    10 00 Data 1, byte 2
    11 00 Data 1, byte 3
    12 00 Length 2
    13 00
    14 FD Data 2, byte 0
    15 10 Data 2, byte 1
    16 00 Data 2, byte 2
    17 C1 Data 2, byte 3