Description

Links are connections between LD objects (contacts, coils and FFBs etc.).

There are 2 different types of links:

  • Boolean Links

    Boolean links consist of one or more segments linking Boolean objects (contacts, coils) with one another.

    There are different types of Boolean links as well:

    • Horizontal Boolean Links

      Horizontal Boolean links enable sequential contacts and coil switching.

    • Vertical Boolean Links

      Vertical Boolean links enable parallel contacts and coil switching.

  • FFB Links

    FFB connections are a combination of horizontal and vertical segments that connect FFB inputs/outputs with other objects.

Connections:

General Programming Notes

Attention should be paid to the following general programming notes:

  • The data types of the inputs/outputs to be linked must be the same.

  • Links between parameters with variable lengths (e.g. ANY_ARRAY_INT) are not allowed.

  • Several links can be connected with one output (right-hand side of one contact, one coil or one FFB output). However, only one link can be connected with an input (left-hand side of one contact, one coil or one FFB output).

  • Unconnected contacts, coils and FFB inputs are specified as "0" by default.

  • Links may not be used to create loops since the sequence of execution in this case cannot be clearly determined in the section. Loops must be created using actual parameters (see Non-Permitted Loops).

Notes on Programming Boolean Links

Notes on Programming Boolean Links:

  • Overlapping Boolean links with other objects is not permitted.

  • The signal flow (power flow) is from left to right for Boolean links. Therefore, backwards links are not allowed.

  • If two Boolean links are crossed, the links are connected automatically. Since crossing Boolean links is not possible, links are not indicated in any special way.

Notes on Programming FFB Links

Notes on Programming FFB Links:

  • At least one side of an FFB link must be connected with an FFB input or output.

  • To differentiate them from Boolean links, FFB links are shown with a doubly thick line.

  • The signal flow (power flow) in FFB links is from the FFB output to the FFB input, no matter which direction they are made in. Therefore, backwards links are allowed.

  • Only FFB inputs and FFB outputs may be linked to one-another. Linking more than one FFB outputs together is not possible. That means that no OR connection is possible in LD using FFB links.

  • Overlapping FFB links with other objects is permitted.

  • Crossing FFB links is also permitted. Crossed links are indicated by a "broken" link.

  • Connection points between more FFB links are shown with a filled circle.

  • To avoid links crossing each other, FFB links can also be represented in the form of connectors.

    The source and target for the FFB connection are labeled with a name that is unique within the section.

    The connector name has the following structure depending on the type of source object for the connection:

    • For functions: "Function counter/formal parameter" for the source of the connection

    • For function blocks: "Instance name/formal parameter" for the source of the connection

    • For contacts: "OUT1_sequential number"

Vertical Links

The "Vertical Link" is special. The vertical link serves as a logical OR. With this form of the OR link, 32 inputs (contacts) and 64 outputs (coils, links) are possible.