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S7 300 integer to real conversion
How do you convert an integer format to real format in the S7 300 CPU's?
By Luiz Rodriguez on 4 September, 2009 - 12:26 am

I need to convert and integer number from a PIW to a real number. What is the easiest way to do this. I don't see any standard function that is capable of converting this.

Hi, You need to convert int to double then double to real i.e.

l piw 123 //int
itd //int to dint
dtr //dint to real
t md 0 // store result in double word

you can do this in ladder using d_int and di_r


By Schneider Electric Italy on 4 September, 2009 - 12:50 pm

L xx
T yy

By Jan Steen Nielsen, Denmark on 11 September, 2009 - 2:05 pm

You may also use S7 standard function-blocks:
"I_DI" followed by "DI_R"
To convert back from REAL to INT you use
the command "RND":
Load <REAL> become: L <REAL>
Round become: RND
Transfer <INT> become: T <INT>
These 3 commands goes fine, if you first ensure
that <REAL> is within the limits
from -32768.0 to +32767.0

Please note that Siemens use reverse polish
calculation. Example, if <A> and <B> are REAL:
L <A>
L <B>
T <A+B>

Good luck
Jan Steen Nielsen
L-N [at]

By david mertens on 14 September, 2009 - 3:14 am

I think you are looking for the SCALE function. This function converts the input of an analog input card to the engineering units you specify. This is a standard library block available in step 7. There is also an UNSCALE function for driving analog outputs (Real to PQW).