Siemens LOGO! Series Manual page 77

Note
Although you have four inputs available for logic operations (Page 142), most of the views
will only show three inputs for reasons of clarity. You program this fourth input and assign
parameters just like you do with the other three inputs.
To create a circuit logic in LOGO!, start at the circuit output.
The output is the load or relay that is to be switched.
Convert the circuit logic into blocks by working through the circuit, starting at the output and
ending at the input:
Step 1: The make contact S3 is interconnected in series to output Q1 and to a further circuit
element. A series connection corresponds with the AND block:
Step 2: S1 and S2 are connected in parallel. A parallel circuit corresponds with the OR block:
Unused inputs
The circuit program automatically assigns the unused connectors a status that ensures
proper functioning of the relevant block. If you like, you can label unused connectors with an
'x' identifier.
In our example we shall use only two inputs of the OR block and two inputs of the AND
block; the relevant unused third and fourth inputs are identified at the connector with an 'x'.
Now connect the I/O to LOGO! .
Wiring
Connect the switches S1 to S3 to the screw terminals of your LOGO! :
● S1 to connector I1 of LOGO!
● S2 to connector I2 of LOGO!
● S3 to connector I3 of LOGO!
The output of the AND block controls the relay at output Q1. The load E1 is connected to
output Q1.
LOGO!
Manual, 04/2011, A5E03556174-01
3.4 From circuit diagram to LOGO! program
Programming LOGO!
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