Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 113)

Chapter 6
Programming Overview
6–16
Applying Ladder Logic and Instruction List
In the following illustration, the electromechanical circuit shows PB1 and
PB2, two push buttons, wired in series with an alarm horn. PB1 is a
normally open push button and PB2 is normally closed. This same circuit is
shown in ladder logic by two contacts wired in series with an output.
Contact I/0 and I/1 are examine-if-closed instructions.
➀ (For more
information on this instruction, refer to page 8–3.)
Instruction List Program
LD I/0
AND I/1
OUT O/1
Electromechanical Circuit
Alarm
Horn
PB1 PB2
1
] [ ] [ ( )
O
1
I
Ladder Logic Program
0
I
➀
Contact I1 would be an examine-if-open instruction ( ]/[ ) if PB2 was a normally open electromechanical circuit.
The table below shows how these circuits operate. The table shows all
possible conditions for the electromechanical circuit, the equivalent state of
the instructions, and the resulting output state.
If PB1 is: I/0 state is: And PB2 is: I/1 state is: Then the Alarm Horn (O/1) is:
not pushed 0 not pushed 1 silent
not pushed 0 pushed 0 silent
pushed 1 not pushed 1 alarm
pushed 1 pushed 0 silent