Siemens S7-1200 - Ladder Logic (LAD)

Programming concepts
6.5 Programming language
S7-1200 Programmable controller
180 System Manual, 03/2014, A5E02486680-AG
6.5.1
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
move.
STEP 7 does not limit the number of instructions (rows and columns) in a LAD network.
Note
Every LAD netw
ork 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.