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Special Functions; Designation Of The Inputs - Siemens LOGO! Manual

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LOGO! functions

4.3 Special Functions

Special Functions
Because of their different input designation, you can see right away that there is a difference
between the special functions and basic functions. Special functions (SFs) contain timer
functions, retentive functions and various parameter assignment options, which allow you to
adapt the circuit program to suit your own requirements.
This section provides you with a brief overview of input designations and with some
particular background information on SFs.

Designation of the inputs

Logical inputs
Here, you will find the description of the connectors you can use to create a logical link to
other blocks or to the inputs of the LOGO! unit.
● S (Set):
A signal at input S sets the output to logical "1".
● R (Reset):
The reset input R takes priority over all other inputs and resets the outputs.
● Trg (Trigger):
This input is used to trigger the start of a function.
● Cnt (Count):
This input is used for counting pulses.
● Fre (Frequency):
Frequency signals to be evaluated are applied to this input.
● Dir (Direction):
This input determines the direction, + or -.
● En (Enable):
This input enables a block function. When this input is "0", other signals to the block will
be ignored.
● Inv (Invert):
A signal at this input inverts the output signal of the block.
● Ral (Reset all):
All internal values are reset.
Unused logical inputs of special functions default to logical "0".
Connector X at SF inputs
SF inputs connected to connector x are set low. That is, the inputs carry a 'lo' signal.
Manual, 10/2017, A5E01248535-AA


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