ANY as the OUTPUT

Hello!

My question is a bit theoretical.

As everyone knows from the STEP 7 programming documentation, the ANY pointer can be an output parameter for FC block only.

Despite the prohibition of ANY as VAR_OUT, I can create such output parameter and neither the LAD/FBD/STL editor nor the SCL compiler will give an error.

But I can't figure out, why when I read the ANY OUTPUT in the FC to my temporal structure - I get correct values (S7-type, data type, length, etc.). But the same operation always returns P#L1.0 within the FB.

What is the fundamental difference between FC and FB that doesn't allow the last one have an ANY as an output parameter?

Hello RoVRy

Could you send a pic from error message or write the error message please.?

RoVRy

Despite the prohibition of ANY as VAR_OUT, I can create such output parameter and neither the LAD/FBD/STL editor nor the SCL compiler will give an error.

But I can't figure out, why when I read the ANY OUTPUT in the FC to my temporal structure - I get correct values (S7-type, data type, length, etc.). But the same operation always returns P#L1.0 within the FB.

What is the fundamental difference between FC and FB that doesn't allow the last one have an ANY as an output parameter?

Just to clarify.

You claim creation of an output of the type ANY from an FB, right? If so, then how?

I can't understand this statement: "I read the ANY OUTPUT in the FC to my temporal structure". Do you mean reading of an output of an FC inside this FC?

When describing software issues, posting screenshots of a code is advantageous.

Knowing the software and its version you are using would be also helpful.

Sorry, my bad. Everything is mixed up in my head during a lot of tries to make a workable solution.

Software is PCS 7 v8.1 SP1.

Hello.

[ For the FC ]
The input sees the reference of the input. Therefore the ANY can interpret the IB128 address.

The output of the FC is only a carrier of the value. The output is internal to the FC is temporary storage. The link to the outside is per value and not per reference. An output should be handled as write-only.

[ For the FB ] 
The values of the outside is linked to the inside through the instance DB. In this case it is DB384. When the Any assignment in the code reads the input, it in fact reads the instance address: DB384.DB0. The same also applies to the output.

The link to the outside is per copy of value and not linked per reference. If the "In" parameter were to change from BYTE to ANY, the situation changes. The address description of the linked tag is then exposed.

Yes, it's all understandable except the one thing: what is "previous local data" (V area = 16#87) and where is it comes from?

And let's go further: let's change "In" and "Out" inside FC from BYTE to ANY. The result is on the screenshot.

I can change FB "In" parameter in the same manner, but this trick doesn't work for the "Out". I don't know why and don't see any reasons for such restriction.

RoVRy

Yes, it's all understandable except the one thing: what is "previous local data" (V area = 16#87) and where is it comes from?

And let's go further: let's change "In" and "Out" inside FC from BYTE to ANY. The result is on the screenshot.

I can change FB "In" parameter in the same manner, but this trick doesn't work for the "Out". I don't know why and don't see any reasons for such restriction.

The FC output is temporarily stored in a local memory area. This local area is the the secondary local area, where the primary local area is used by the TEMP definitions. It is unfortunate that that area is only named as 'previous'.

In the FC the [value] flows from temporary storage to the tag that is connected to the output. Information flows only in one direction. That information is only the value. The address associated with that tag is not known to the inside of the FC.

Even with data type ANY, the situation would not have changed. The flow of information is outward and the information is a value (not an address). It just happens to be that the value is a pointer that reference to an address.

What you want to do in reading the address of the tag that is connected on the output is simply not possible. But knowing the address through the input, makes it possible to indirectly write a value to that address. You can use the block move instruction for example.

In my view, if you want to make the outside interface simple, the block should simply receive a number as an input. the pin would be named "inByteNr" and "outByteNr".

The S7-1500 do have other tricks where you can link data by reference.. but that is not what you have to work with. The clay you have does not mould that way.