Lenze DDS v2.3 - Manual (Page 58)

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Programming languages
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DDS EN 2.3
4.7 Ladder diagram (LD)
The Ladder Diagram is a graphically oriented programming language which is similar to the principle
of an electrical circuit.
LD is used for the design of logic circuits and also allows the creation of networks as in FBD. LD is
therefore perfectly suited to control calls for other organization units.
LD consist of several networks.
•
A network is limited on the left and on the right by a vertical power cable. In-between is a
circuit diagram consisting of contacts, coils and connection lines that transmit the status
” ON” or ” OFF” (TRUE or FALSE) from left to right.
Example of a network in LD:
4.7.1 Contact
Every network in LD consists of a network of contacts on the left-hand side, which transmit the
status ” ON” or ” OFF” from left to right (variable value TRUE or FALSE).
If a Boolean variable of a contact has the value TRUE, the status ” ON” is transmitted via the
connection line from left to right. Otherwise, the right-hand connection is set to ” OFF” .
Parallel or series connection
•
Contacts can be connected in parallel. In that case one of the parallel branches must transmit
the value ” ON” to ensure that the entire parallel branch transfers the value ” ON” .
•
Contacts can be connected in series. In that case, all contacts must transmit the status ” ON”
to ensure that the last contact transmits ” ON” .
Negation
A contact can also be negated. It is then identified with a slash in the contact symbol. The contact
then transmits the input status if its status is ” OFF” (FALSE).
4.7.2 Coil
Any number of so-called coils (represented by brackets) are listed on the right-hand side of a
network in LD.
•
A coil transmits the connection value from left to right and copies it into an associated
Boolean variable.
•
The input line can be set to ” ON” or ” OFF” (depending on the Boolean values TRUE or
FALSE
).
•
Coils can only be connected in parallel.
Negation
Coils can also be negated (shown by a slash in the coil symbol). In that case, the coil copies the
negated value to the associated Boolean variable.
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