Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 53)

Chapter
6
6Ć1
RelayĆtype Instructions
This chapter describes:
relay-type instructions
how to define conditions before an action takes place
A program is a list of instructions that the processor executes. These
instructions can examine or change the status of bits in the data table of the
processor. The status of these bits can determine the operation of
other instructions.
The program you specifies the order of things you want done in your
application and the conditions that must be met before those things are done.
For example, if you want a solenoid energized when a limit switch is closed,
you specify:
Condition: if limit switch is closed
Action: energize solenoid
Programming logic differs from relay logic in an important way. Programming
logic is only concerned with whether or not conditions have been met. These
conditions may be open or closed input or output devices. We must have a
continuous or unbroken path or true logic conditions for an action to be taken.
The number of conditions is not important. There can be none, one, or many
conditions preceding an output action.
Perhaps an example might make this clearer:
C1
True
C2
True
C3
True
A
True
False
Here, a series of conditions (C2, C2, C3) must be true before action A
is performed.
Chapter Objectives
Programming Logic