Old S7-300 SLC code - what's going on ??

HI

My SLC understanding is not perfect yet, and have been over the manuals again and again, but I am digging true some old code and I have this little section that I am not totally sure about:

L DBW 5
SLW 3
LAR1
L DBW [AR1,P#0.0]
T MW 5

Does this make sense to anyone ?

If we for example say the value of DBW 5 = 2

How would this workout ?

/Holmux

Hello ,
The code is not complete, but I will try to explain the meaning.

Siemens indirect addressing

1. load value from DBxx.DBW5 ()Is there earlier command OPN DBxx? on code)
2. SHL 3 (SHIFT LEFT 3 -> INT to pointer format conversion, same as multiple with 8, pointer has 8bits and word address -> so now we look word address. ex. DBW5 = 2 -> SHL 3 -> 16 (Pointer points to second word, if you don't SHL3/multiple8 then pointer points to 2nd bit...)
3. Load pointer to AR1
4. Load from DBW address with pointer , P#0.0 is offset (ex. AR1 =16 + offset 0.0 => Load pointer = 16 (points 2nd word)-> load DBW2)
5. transfer loaded value to MW5

same if DBW5 has value 3 or 4, now we load indirectly 3rd and 4rd word to MW5

Thanks for the help

I have been searching high and low for some more detailed information on the "Offset" function, but reading the Siemens help file convinced me that they drink a lot of beer in Germany, very confusing

To be honest I don't have a clear view of the basic's of the Offset function, I remember reading a good article about the function way back, but can't seem to find it again.

Can you point me in the right direction ?

/Holmux

For start:

http://www.plcdev.com/siemens_s7_indirect_addressing

http://www.plctalk.net/qanda/showthread.php?t=3184

Jesper's example is pretty good,

Search Forum members: L D[AR2,P#0.0] posts, he knows pretty much of siemens

http://www.plctalk.net/qanda/showthread.php?t=66380