Selecting The Programming Language - Siemens SIMATIC S7 System Manual

instructions in an interrupt OB, use a DIS_AIRT instruction to delay any interruption (an
interrupt OB or a communication interrupt from an HMI or another CPU) until an EN_AIRT
instruction is executed.
Note
The use of the DIS_AIRT instruction delays the processing of interrupt OBs until the
EN_AIRT instruction is executed, affecting the interrupt latency (time from an event to the
time when the interrupt OB is executed) of your user program.
5.5

Selecting the programming language

You have the option of choosing either the LAD (ladder logic) or FBD (Function Block
Diagram) programming language.
LAD programming language
LAD is a graphical programming language. The representation is based on circuit diagrams.
To create the logic for complex operations, you can insert branches to create the logic for
parallel circuits. Parallel branches are opened downwards or are connected directly to the
power rail. You terminate the branches upwards.
LAD provides "box" instructions for a variety of functions, such as math, timer, counter, and
move.
Consider the following rules when creating a LAD network:
● Every LAD network must terminate with a coil or a box instruction. Do not terminate a
● You cannot create a branch that could result in a power flow in the reverse direction.
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
network with either a Compare instruction or an Edge-detection (Positive-edge or
Negative-edge) instruction.
Programming concepts
5.5 Selecting the programming language
The elements of a circuit
diagram, such as normally
closed and normally open
contacts, and coils are
linked to form networks.
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