S7 operate SR bit on start up?

Hi

I have seen this done on RSLogix, where you can operate a 'One Shot' Status bit on the first run of the program.
I want to set a SR Flip Flop on start up of a program, after the first cycle I dont want it to operate again, how can I achieve this with Step7?

Thanks

Darren

I'm not sure if I fully understand what you want. Are you looking for a Flag that signals that you are on the first time through in OB1 (or any other Block for that matter)?

If so, you can realise it pretty easily by simply setting a Marker Bit in OB100 and then resetting it as the last command in OB1. However, that sounds a bit too easy to be true, so I probably haven't really understood what you need.

Set the bit in the start-up OB (OB100?), then reset it as the last rung of the cyclic OB (OB1?)

Thanks, that sounds like what I need, although you seem to talk as if I should already have an OB100 set up? Are there any more OB's I need to consider? My structure so far is OB1 and some function calls.

I am new to S7

Darren

S7 uses several types of OB blocks for programming, and different CPU's offer different OB's; if you look them up in the online help, you will find a listing and description of each.

OB1 is the Cyclic block, and is scanned top to bottom, then repeats.

OB100 is executed on power-up and switch to run mode once before OB1 begins executing.

There are also other OB's that can be set up as timed interrupt blocks, error handling blocks, time-of-day interrupt blocks, and many others.

Thanks Guys, that has worked a treat
Cheers
Darren

sm0.0

You can use special memory bit sm 0.0
This goes high in the first scan cylce

You can use special memory bit sm 0.0
This goes high in the first scan cylce

Click to expand...

Yes if you were using the 200 Series, But no if were talking 300/400.

Regards