S7-300 STL CRC calculation

Hello,I understand that the code bellow add value of bytes together,but why there is XOW istructinon????

OPN DB [#tmp_DB_NO]
L #tmp_LOOP // -> Loopcounter
LOOP: T #tmp_LOOP
L B [AR1,P#0.0] // loading the values in DB
L #tmp_CRC_TEMP
// XOW
+I
T #tmp_CRC_TEMP

+AR1 P#1.0 // increase the addressregister on next byte in field

L #tmp_LOOP //-> doing so often like in amount in Any Pointer is described
LOOP LOOP


Thanks a lot...

It is not active in the code you supplied? Or did you add the // ?

There are many different methods to calculate a CRC. Two simple ones are to XOR the data together, or to add the data together.

As boneless says, the XOW is commented out, and not active, in your code. It is possible they used to use the XOR method, and switched to addition.

I commented it out,because it did not work properly with it....manufacturer sent me a new remade program and it did not communicated with one tester until I did it.....and so I could not find a reason for using XOW...probably it was only mistake....Anyway Thanks a lot

That isn't a CRC calculation. It is simply a checksum.

Hello,Yes I see it is simply checksum (but FB is named CRC calculation)...
by the way is there any good implementation of CRC for simatics or some good tutorials about CRC?Thaks

Just search. There are many different types of CRC. There are a lot of examples in C. The fastest ones use tables.