siemens plc

[jugenzhu1963]

hi,everybody

I am learning siemens plc(s7-300) now. I don't know how to manipulate the bit memory. For Example how i can make bit M0.0 always ON. Please help me.

Thank you

 

[krk]

SET //Set RLO (to 1)
=M0.0 //Assign to bit

 

[lauu]

M0.0 M0.0
----|/|---------------()-
| |
| M0.0 |
--| |---

 

[SimonGoldsworthy]

Hopefully the two other posts have answered your question. (Another answer is that you can't - if some other processing decides to clear M0.0, then it will be clear until the next time the set instructions are executed)

 

[S7Guy]

Another thing to remember is that an "always on" bit really isn't necessary with Siemens S7. I've written tens of thousands of lines of code, and haven't used one yet. Instead, take advantage of the "SET" and "CLR" commands, which directly affect the RLO.

 

[stplanken]

Another thing to remember is that an "always on" bit really isn't necessary with Siemens S7.

Interesting. I use AlwaysOn bits to temporarily bypass one or more contacts in ladder or disable (parts of) a rung, without actually removing any logic. Only in LAD, in STL I have no use for it.

 

[Rack Failure]

[stplanken]Interesting. I use AlwaysOn bits to temporarily bypass one or more contacts in ladder or disable (parts of) a rung, without actually removing any logic. Only in LAD, in STL I have no use for it.

I have done the same as stplanken using always ON (M0.0) and always OFF (M0.1)flags. The flags are set up in OB1. Anyone else do the same?

Homer

 

[rdrast]

I have done the same as stplanken using always ON (M0.0) and always OFF (M0.1)flags. The flags are set up in OB1. Anyone else do the same?

Homer

Hrm... maybe it's just me, but wouldn't it be more intuitive to use M0.0 for the 'Always OFF' state and M0.1 for the 'Always ON' state?

 

[Rack Failure]

Rdast
Oops a typo, should've been more carefull.
BTW how do you do a quote box like you've done? Tried it in my last post but hasn't worked.

 

[geniusintraining]

Rdast
Oops a typo, should've been more carefull.
BTW how do you do a quote box like you've done? Tried it in my last post but hasn't worked.

click here

 

[bkottaras]

Always OFF, always ON

Hrm... maybe it's just me, but wouldn't it be more intuitive to use M0.0 for the 'Always OFF' state and M0.1 for the 'Always ON' state?

I use the same setup in order to debug as well as enable disable certain functions and rungs of logic on the fly.
Yes, M0.0=always OFF, M0.1=always ON.