Siemens Industry Online Support
Siemens AG
Entry type: FAQ Entry ID: 14761527, Entry date: 12/21/2010

How can you install block protection for an S7-SCL block?

  • Entry
  • Associated product(s)

You can set a block protection for blocks by adding the attribute KNOW_HOW_PROTECT when programming the block. 

Activating block protection has the following effects. 

  • If you later open a compiled block with the incremental STL editor, the statement part of the block cannot be viewed.
  • The negotiation part of the block will only show the variables of declaration types VAR_IN, VAR_OUT and VAR_IN_OUT. The variables of the negotiation blocks VAR and VAR_TEMP remain hidden. 

When entering the block protection, the following applies.

  • The keyword is KNOW_HOW_PROTECT. It is entered before all other block attributes. 
  • OBs, FBs, FCs and DBs can be protected this way. 

Proceed as described in the table below to install block protection for an S7-SCL block.

No. Procedure
1 In the source folder of your STEP 7 program you open the S7-SCL source.
2 Insert a line with the attribute "KNOW_HOW_PROTECT" in the declaration part of the S7-SCL source.

Fig. 01

3 Save and compile the S7-SCL source.
4 Remove the S7-SCL source from the source folder. This activates block protection for your S7-SCL program.
5 Save your S7-SCL source.

A padlock is displayed on the block icon in the SIMATIC Manager to indicated that the function is protected.

Fig. 2: Icon for a protected function

After the deletion of the S7-SCL source, the block cannot be changed anymore. Likewise, you can no longer deactivate the Know How protection.
More information on the topic of block protection ("Know_How_Protect") for DBs, FBs and FCs is available in Entry ID 10025431.

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit