Ladder Logic (Lad) - Siemens S7-1200 System Manual

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Programming concepts

6.5 Programming language

Ladder logic (LAD)

The elements of a circuit diagram, such as normally closed and normally open contacts, and

coils are linked to form networks.

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

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

Every LAD network must terminate with a coil or a box instruction.

Consider the following rules when creating a LAD network:

● You cannot create a branch that could result in a power flow in the reverse direction.

● You cannot create a branch that would cause a short circuit.

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG