Chapter 5
Ladder Program Basics
5–4
In the previous section on logical continuity, you have seen examples of
series (And) logic. This means that when all input conditions in the path are
true, energize the output.
Example – Series Inputs
A
B
C
In the above example, if A and B are true, energize C.
Another form of logical continuity is Parallel (OR) logic. This means that
when one or another path of logic is true, energize the output.
Example – Parallel Inputs
A
C
B
In the above example, if A or B is true, energize C.
Use branching to form parallel logic in your user program. Branches can be
established at both input and output portions of a rung. The upper limit on
the number of levels which can be programmed in a branch structure is 75.
The maximum number of instructions per rung is 127.
Series Logic
Parallel Logic
