String configuration with S7-300 TCP Driver

[J.Fournier]

Hi,

Im trying to configure a string to communication with an S7-300 Siemens PLC. Im am using the driver S7 ISO over TCP/IP.

The string adress in the PLC is "db155.dbx40.0 byte 26". I could not find any information about the format anywhere in the documentation. I tried a lot of variations, but none of them would work, I always get the "Invalid adress format" error message.

Any clue on how to format the adress?

Thanks!

[Ron L.]

There is some documentation somewhat hard to find in iX Developer. See this FAQ for details.
http://ixtalk.beijerelectronics.us/view ... hp?f=8&t=4

In that documentation you will find the addressing syntax.

[J.Fournier]

Hi Ron,

I already went through the documentation of the driver. It mentions how to configure a digital signal, and an analog signal. There is no mention about char or string. However, there is those 2 notes :

Note: When storing ASCII values in 16-bit numbers the eight least significant bits contain the second ASCII code.

Note: The first two bytes in a string only contain information about the string.

But still, how do I format the adress of a string? Should I put the starting adress of the 1st word? Or the first byte? Or the first bit?

Also, how can I control the length of the string? Is it by using the data type in the tag declaration, or the adress should contain the length itself?

A syntax that currently compiles is the following. This is a string of 24 char starting at byte 60.

Code: Select all

Data type : STRING[24]         Adress : DB155.DBB60

Would this work? I currently does'nt have access to the PLC, so it will be hard to test.

Thanks,

[bjornidar]

Hi,

didn't find any answer to this on any forum, so I thought I would post my solution.
NB! This solution splits a string into several INT's.

In iX you have to configure the tag with address DBxx.DBWyy , and if you wan't to read as well as write a string, you also have to set type STRING for not only the controller, but also the "Tag"-section.

You would probably need to use script to set the string value to the tag.

I also encountered that when I wanted to use the string and read values from it there was no values the first time. There for I had to add tag.Read() in the startup screen's script.

In Siemens you have to use two built-in functions, the first two bytes of the string value can't contain any valuable data, as Siemens use these for string length.
First you use FC26 (MID) and set P = 1 (for the first word, byte, ...), the length depends on how many strings you wan't to read at a time.
The output from FC26 should be a new DB string with the length you wan't.



Next you put this string as an input to FC38, this convert the string to an INT.