Technical data

Basics of Creating Logic Blocks
10.6 Editing FBD Elements in the Code Section
Programming with STEP 7
260 Manual, 05/2010, A5E02789666-01
10.6.2 Rules for Entering FBD Elements
You will find a description of the programming language "FBD" in the "Function Block Diagram for
S7-300/400 - Programming Blocks" manual or in the FBD online help.
An FBD network can consist of a number of elements. All elements must be interconnected
(IEC 1131-3).
When programming in FBD, you must observe a number of rules. Error messages will inform you
of any errors you make.
Entering and Editing Addresses and Parameters
When an FBD element is inserted, the characters ??? and ... are used as token characters for
addresses and parameters.
• The red characters ??? stand for addresses and parameters which must be connected.
• The black characters ... stand for addresses and parameters which can be connected.
If you position the mouse pointer on the token characters, the expected data type is displayed.
Positioning Boxes
You can add standard boxes (flip flops, counters, timers, math operations, etc.) to boxes with
binary logic operations (&, >=1, XOR). The exceptions to this rule are comparison boxes.
No separate logic operations with separate outputs can be programmed in a network. You can,
however, assign a number of assignments to a string of logic operations with the help of a branch.
The following figure shows a network with two assignments.
The following boxes can only be placed at the right edge of the logic string where they close the
string:
• Set counter value
• Assign parameters and count up, assign parameters and count down
• Assign pulse timer parameters and start, assign extended pulse timer parameters and start
• Assign on-delay/off-delay timer parameters and start