Simatic TIA Portal know-how

I predict that in the chapter, I will write the descriptions in my own words, as if I were trying to explain things to a friend. The description may not be professional this way, but my goal is for anyone who reads to understand what is described.

FCs are programming blocks that do not require static variables, that is, they do not need internal information that would be stored from one cycle to another. It is therefore not necessary to assign data blocks, i.e. DBs, to FCs.

In the references, I denote FCs as follows: _FC_

for example: _FC_ Result := ABS (Value);

• double click to „Add new block”
• chose „Function”
• type a new name

FBs are a bit more complex modules than FCs. FBs are able to define cyclical variables, these are „static” variables. These are not actually stored in the FB, but will be assigned a datablock (DB) to each FB and it will store these variables. These DBs should be called IDBs (instant datablocks) because, unlike global DBs, they are assigned to a specific FB. In addition to storing variables, IDBs are also suitable for storing embedded FBs, this will be discussed later. The IDB will be assigned to a given SC during the first call.

In the references, I denote FBs as follows: _FB_

for example: _FB_ RetVal (INT):= BLKMOV (SRCBLK := source block (VARIANT); DSTBLK ⇒ destination block (VARIANT); ENO ⇒ operation enable );

• double click to „Add new block”
• chose „Function block”
• type a new name

When we open the newly created Fc or FB (FB in the example) we will see the following image:

Field reports:

Calling FCs is easier:

1. the part of the program (FC, FB or OB) from which the FC is to be called must be opened.
2. drag-and-drop the FC from the „instructions” window, or simply plug it in. For example, after indentation, „LN” FC looks like this: LN (_real_in_)
3. you need to know, for example from here that the „LN” FC is calling floating-point numbers, ie REAL or LREAL.
4. the return value must also be given, eg: out:= LN(in); where in and out are REAL.

When calling FBs, we have two options:

1. each invited sub_FB receives its own IDB
2. sub_FBs are treated as an embedded function and their data area will be „taped” to the IDB of the calling FB.

Let's see this through examples, let's take one of the most commonly used methods, TON:

First method, call with separate IDBs:

	Using two TON FBs, both calling their own IDBs
	Content of one of the IDBs

Second method, call embedded FBs:

	In the case of embedding, the functions must be called from the „static” block of the calling FB (just type „TON” for the „data type”. FBs must be called in the program in much the same way, of course the DB call must be omitted.
	The image shows the data of the embedded FBs in the IDB of the calling FB. The great advantage of this method is that the program is easy to import / export / copy, as you only need one FB definition.

By default, the TIA portal turns on the „optimization” attribute of DBs, which means that the order of variables in DBs is automatically optimized.

In many cases, this causes serious problems when the given variables have to remain in predefined positions, such as OPC, or typically any similar communication (Modbus, PN, ..) DB. For example, the BLKMOV command does not work with optimized DBs either.

To deactivate, right-click on the DB and select Properties… and then Attributes:

The „optimized block access” attribute in the menu must be turned off.

For generated DBs, the {S7_Optimized_Access: = 'TRUE'} entry should be modified as follows: {S7_Optimized_Access: = 'FALSE'}.

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