Use of memory/marker bits in an FB on S7

[AndrewM]

Hi

Hope someone can help(Newbie Question), I vaguely recollect reading somewhere that you can't or shouldn't use memory bits within an FB when using declarations on an S7 is this correct, I had a quick flick through the Step7 manual but couldn't see anything obvious.

Regards Andrew

 

[L D[AR2P#0.0]]

....use memory bits within an FB when using declarations on an S7...

Unfortunately this does not make any sense. Can you give a concrete example of what you want to do ?

 

[AndrewM]

Unfortunately this does not make any sense. Can you give a concrete example of what you want to do ?

Hi L D[AR2,P#0.0]

Sorry for not explaining myself very well, I am not sure exactly how to phrase the question, what I am trying to say is, on a Siemens S7-300 when writing a program with Ladder Logic From OB1 I Call a Function Block FB1 which has ProcessRun delared as an Input, essentially what I would like to know is the following M5.0 address legal/correct?


_#ProcessRun___M5.0_________________#Pump1
------| |---------| |-----------------------( )


Regards Andrew

 

[L D[AR2P#0.0]]

Yes, this is legal.

I presume M5.0 is a global indicator of e-stop or the like.

 

[AndrewM]

Yes, this is legal.

I presume M5.0 is a global indicator of e-stop or the like.

Thanks for the reply, I was actually hoping to use it as part of a sequence control, I have 4 tanks that require filling/emptying/mixing and heating sequentially, my first thought was to use say MW4 set to 1 and then shift left at the end of each stage to disable the current stage and enable the next stage, does this make sense and would it be a good way of doing such a task?

Regards Andrew

 

[TurpoUrpo]

Is the fb intended for multiple instance? is that data needed elsewhere in the program?

 

[L D[AR2P#0.0]]

Thanks for the reply, I was actually hoping to use it as part of a sequence control, I have 4 tanks that require filling/emptying/mixing and heating sequentially, my first thought was to use say MW4 set to 1 and then shift left at the end of each stage to disable the current stage and enable the next stage, does this make sense and would it be a good way of doing such a task?

Regards Andrew

You are writing one FB and calling it 4 times for each tank?

If so I would use STAT variables for stage control using SET/RESET as each stage progresses.

 

[AndrewM]

You are writing one FB and calling it 4 times for each tank?

If so I would use STAT variables for stage control using SET/RESET as each stage progresses.

I have actually got 4 FB's 1 for each tank as there are subtle differences to what happens in each.

 

[AndrewM]

You are writing one FB and calling it 4 times for each tank?

If so I would use STAT variables for stage control using SET/RESET as each stage progresses.

Thanks for all the replies,

Its got me thinking, if you set/reset a STAT variable to enable stages in 1 FB, Is it OK to set/reset a global variable to enable a stage in a different FB.

 

[TurpoUrpo]

Yes.

Also you can access other fb's variables trough its db.

 

[L D[AR2P#0.0]]

Its got me thinking, if you set/reset a STAT variable to enable stages in 1 FB, Is it OK to set/reset a global variable to enable a stage in a different FB.

You could add these variables to the FB interfaces (IN_OUT) and pass them between each other.

 

[AndrewM]

Yes.

Also you can access other fb's variables trough its db.

Hi TurpoUrpo

I must admit I hadn't thought of doing it this way, is this a popular method?

Its for some coursework I am doing, so I don't want to be doing anything non-standard!

Regards Andrew

 

[L D[AR2P#0.0]]

You can roll Siemens anyway you like, so non-standard doesn't apply (unless you can point us to a written standard that you must adopt)

 

[L D[AR2P#0.0]]

... unless you mean you need to keep it within the comprehension level of the person assessing the course work!

 

[L D[AR2P#0.0]]

Its for some coursework I am doing, so I don't want to be doing anything non-standard!

How will you test your implementation - using PLCSIM or some real h/w ?