Indirect Addresing

Hi can I use indirect addressing in Step7?
For example when using RSLogix 500 you enter F8:[N7:1] giving the double word location according with the value of N7:1

I was wondering if I could enter somenthing similar in Step7

Hello PLC-friend;
There have been many discussions on this site about indirect addressing with S7 PLCs. For example, follow this link:

http://www.plctalk.net/qanda/showthread.php?t=7641&highlight=s7+INDIRECT+ADDRESSING

Basically, you cannot do it with LAD instructions. You must use STL programming in order to affect a pointer + offset structure to your addressing. If you open a S7 programming manual, look for instruction LAR1 and LAR2 (load area pointer) which is also used in indexed addressing.

On Siemens's website you have access to much information on addressing with pointers. Look at this link, for example:

http://support.automation.siemens.com/-snm-0135109872-1116758784-0000002349-0000007245-1118116949-enm-WW/llisapi.dll?query=Indirect+addressing+S7&func=cslib.cssearch&content=skm%2Fmain.asp&lang=en&siteid=cseus&objaction=cssearch&searchinprim=0&nodeid0=4000024

I remember S7Guy had a very interesting application that was available on the download site, here. It was called Conveyor.zip, and used Indirect symbolic addressing in a very creative way.

hope this helps,
Daniel Chartier

Indirect Addressing Help

There is actually some pretty good help in step 7 under the STL help.