How To Use indirect addressing In S7-300

[Husanto 0]

Hi all, I have some problem about converted LIR instruction in S5 to S7. I already study how that function work but the problem is can in S7 we use absolut memory inderect addressing?? This a sample code in S5 that's i'm going to convert : C DB 4 L KH 7E00 T DW 70 L KF +4 SLW 1 L DW 70 +F after execution =====> ACCU1 = 7E08 <==> how to compare this absolut area in S7 LIR 0 T FW 240 ======> FW240=???? if anybody know how to convert that's instruction, please let me know... Thanks Vic

[Hammy 0]

Hi, This link is to the Siemens S5 Forum for a question very like yours explaining that the command cannot be used in S7 but with advice on how to get around this. Hope it helps. https://www.automation.siemens.com/WW/forum...mp;PostID=54427

[Groo 7]

You've already been told on another forum that you cannot repeat the same in Step 7, also you forgot to mention once more that the PLC is a 95u, which is very important as the memory maps are different in all the S5 PLC's. 7E00 = DB0 DW0 7EFF = DB0 DW254 so 7E08 = DB0 DW4 DB0 and DB1 are reserved DB's in the 95u. DB1 is where you can set up your on board items, like the counters, analogue inputs etc.. DB0 is a system DB, the contents of which are not listed in the 95u manual. what this is doing is anyone's guess, the only way to get a clue is to either find a detailed description of DB0 or to try to identify what the code is doing. It is likely there is no exact substitution in a S7-300 PLC. Knowing what a LIR instruction can do is not enough here, you have to know what that peice of code is linked with and the guess at what it is doing, only then can anyone help. That snippet of code is useless unless you have the detailed description of DB0.