Rules for Constructing Simple, Series, and Parallel Networks in LAD (GS 3.3)

Rules about Placing Contacts

Each network must begin with a contact.

You cannot terminate a network with a contact.

Rules about Placing Coils

You cannot begin a network with a coil; coils are used to terminate a network of logic. A single network can have several coils, as long as the coils exist on parallel branches of that particular network. You cannot place more than one coil in a series (that is, you cannot have multiple coils on a single horizontal line of a network).

Rules about Placing Boxes

If a box has ENO, power flow extends beyond the box; this means that you can place further instructions after the box. You can have several boxes with ENO in a series on the same rung of a network. If the box does not have ENO, you cannot place any instructions after it.

Network Size Limits

You can think of the Program Editor window as a grid divided into cells (cells are the areas where you can place an instruction, assign a value to a parameter, or draw a line segment). Inside that grid, an individual network can extend no further than 32 cells horizontally or 32 cells vertically.

The graphics below illustrate some of the logic constructions possible in the STEP 7-Micro/WIN 32 LAD editor.

1.This network uses a normal contact ("Start") and a negated (NOT) contact ("Stop"). Once the motor is successfully activated, it latches and remains on until the Stop condition is met.

2.Notice that if the first condition is met, the preliminary output (Output 1) comes on before the second condition is evaluated. You can create multiple rungs that have midline outputs.

3.If the first box instruction evaluates successfully, power flows down the network to the second box instruction. You can cascade multiple ENO instructions in a series on the same rung of the network. If any instruction fails, the rest of the instructions in the series are not evaluated; power flow stops. (Errors are not cascaded through the series.)

4.When the start condition is met, all outputs (boxes and coils) are activated. If one output fails to evaluate successfully, power still flows to the others; they are not affected by the instruction that failed.

See Also:

Micro/WIN Compiler Errors