Reading single bit from word?

Hello,

Does anyone know how read state of single bit from word or struct inside instance DB?

Normally I’m transferring contents of input word to static variables inside DB (struct of bool) using pointers and addressing registers, these technique is very effective, but with S7-300/400. I have no idea how to do this in 1200 cpu. I need states of single bits to make logic based on status word from frequency inverter. I’m using several inverters therefore the best program solution will be to use one FB.

Does anyone have idea?

Thanks.

Hi,

Of course you are right, but this is absolute addressing. I would like make one FB for frequency inverters eg. FB1/DB1 – first drive , FB1/DB2 – second drive, FB1/DB3 – third drive ect. (they are similar). When I put direct address DB1.DBX0.0 it will always point DB1 even if FB1 will be called with DB2 or DB3. I think the only solution is to write 3 FBs with different code inside with absolute addressing (eg. DB1.DBX0.0 in FB1, DB2.DBX0.0 in FB2, DB3.DBX0.0 in FB3). In my case I have 3 inverters so it’s not a big problem. But imagine situation that you have 10 or 20 devices and you have to write 10 or 20 FBs. In my opinion it’s pointless, modifying many blocks will be difficult in the future instead of one and it will consume more PLC memory. Correct me if I’m wrong?

jahhr

Hi,

Of course you are right, but this is absolute addressing. I would like make one FB for frequency inverters eg. FB1/DB1 – first drive , FB1/DB2 – second drive, FB1/DB3 – third drive ect. (they are similar). When I put direct address DB1.DBX0.0 it will always point DB1 even if FB1 will be called with DB2 or DB3. I think the only solution is to write 3 FBs with different code inside with absolute addressing (eg. DB1.DBX0.0 in FB1, DB2.DBX0.0 in FB2, DB3.DBX0.0 in FB3). In my case I have 3 inverters so it’s not a big problem. But imagine situation that you have 10 or 20 devices and you have to write 10 or 20 FBs. In my opinion it’s pointless, modifying many blocks will be difficult in the future instead of one and it will consume more PLC memory. Correct me if I’m wrong?

Hi,

Maha:
I’ve tried to put syntax as you wrote but editor returns me message: “Absolute access to AS1200 is not possible, without specifying a DB”. My FB is NON-symbolic. This works well but in STEP7. I think your second solution will be good, I thought about something like this, but not multi-instance, one FC and global DB with global access (eg. DB1.DBX0.0).

Pegaia:
Thanks for link, yours solution ideally fulfils my requirements. On input I have WORD and I have to transfer it into STRUCT of BOOL [16]. In STL it would be only 2 lines and no problem.

Once again thanks all for help!