ELM409
Pin Descriptions
VDD (pin 1)
hysteresis means that very slow moving or noisy
signals can be accommodated by the ELM409
without needing the signal to be preconditioned by
any external circuitry. (A standard CMOS input
should never have a slowly varying signal applied,
as it may cause excessive currents to flow internally,
but a Schmitt input circuit does not have this
limitation.)
This pin is the positive supply pin, and should always
be the most positive point in the circuit. Internal
circuitry connected to this pin is used to provide
power-on reset of the microprocessor, so an external
reset signal is not required. Refer to the Electrical
Characteristics section for further information.
A, B, and C (pins 2, 3, and 4)
Out (pin 7) and Out (pin 6)
These three pins modify the behaviour of the
ELM409, providing eight different configurations.
They determine whether the output should follow the
input, be a momentary pulse, or toggle the output on
each input transition. As well, they can select either
a standard 25 msec debounce period, or a longer
500 msec one. The longer period may be useful for
some very noisy interfaces, or for situations that
need a slight delay. See the “ELM409 Operation”
section for more details on these options.
The ‘debounced’ and processed signal is output on
pin 7, while the complement of this signal is output
on pin 6. These are high current CMOS drivers, so
will interface to virtually all of the common digital
logic families.
VSS (pin 8)
Circuit common is connected to this pin. This should
be the most negative point in the circuit.
In (pin 5)
The signal that is to be processed is applied to this
pin. Before the signal is ‘debounced’, it is passed
through a Schmitt trigger - a special buffer circuit that
has hysteresis in its gain function. The use of
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 208 mil SOIC surface
mount type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP............................... ELM409P
208 mil SOIC..................................... ELM409SM
All rights reserved. Copyright 2009 by Elm Electronics Inc.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
ELM409DSA
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