Function Block Diagram (Fbd); Scl - Siemens S7-1200 System Manual

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Function Block Diagram (FBD)

Like LAD, FBD is also a graphical programming language. The representation of the logic is

based on the graphical logic symbols used in Boolean algebra.

Mathematical functions and other complex functions can be represented directly in

conjunction with the logic boxes.

STEP 7 does not limit the number of instructions (rows and columns) in an FBD network.

Structured Control Language (SCL) is a high-level, PASCAL-based programming language

for the SIMATIC S7 CPUs. SCL supports the block structure of STEP 7 (Page 172). Your

project can include program blocks in any of the three programming languages: SCL, LAD,

SCL instructions use standard programming operators, such as for assignment (:=),

mathematical functions (+ for addition, - for subtraction, * for multiplication, and / for division).

SCL also uses standard PASCAL program control operations, such as IF-THEN-ELSE,

CASE, REPEAT-UNTIL, GOTO and RETURN. You can use any PASCAL reference for

syntactical elements of the SCL programming language. Many of the other instructions for

SCL, such as timers and counters, match the LAD and FBD instructions. For more

information about specific instructions, refer to the specific instructions in the chapters for

Basic instructions (Page 203) and Extended instructions (Page 283).

You can designate any type of block (OB, FB, or FC) to use the SCL programming language

at the time you create the block. STEP 7 provides an SCL program editor that includes the

following elements:

● Interface section for defining the parameters of the code block

● Code section for the program code

● Instruction tree that contains the SCL instructions supported by the CPU

You enter the SCL code for your instruction directly in the code section. The editor includes

buttons for common code constructs and comments. For more complex instructions, simply

drag the SCL instructions from the instruction tree and drop them into your program. You can

also use any text editor to create an SCL program and then import that file into STEP 7.

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG

Programming concepts

6.5 Programming language

To create the logic for complex operations,

insert parallel branches between the boxes.