Rockwell Automation 9323-S5500D A.I. SERIES MICROLOGIX 1000 AND PLC-500 SOFTW - Manual (Page 111)

MicroLogix 1000 and PLC-500 A.I. Series Software Reference
5-6
Series Logic (AND)
So far you have seen examples of series (AND) logic. When input instructions are in
series, all input conditions in the path must be true for the output to energize.
] [ ( ) ] [
A B C
Series Inputs
In this example, if A and B are true, energize C.
Parallel Logic (OR)
Another form of logical continuity is parallel (OR) logic. When input instructions are
in parallel, one path or another must be true to energize the output.
] [
] [
( )
A
C
B
Parallel Inputs
In the above example, if A or B is true, energize C.
Use branching to form parallel logic in your user program. You can use branching to
avoid redundant instructions, speed up processor evaluation, and provide more efficient
programming. 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 parallel branch
structure is 75. The maximum number of instructions per rung is 128.