ELM440
Pin Descriptions
VDD (pin 1)
waveforms may be applied to this input, as the
input circuitry is of the Schmitt trigger type. The
input frequency can be either 60Hz or 120Hz (as
would be obtained from a full wave rectifier), as
internal circuitry will adjust to each. If this input is
not used, the pin should be connected to either
VDD or VSS.
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.
1Hz (pin 6)
XT1 (pin 2) and XT2 (pin 3)
The output on this pin is a 1Hz signal of
nominally 50% duty cycle.
A 3.579545MHz NTSC television colourburst
crystal is connected between these two pins.
Crystal loading capacitors (typically 27pF) will
also normally be connected between each of the
pins and Vss.
60Hz (pin 7)
The output on this pin is a 60Hz signal of
approximately 50% duty cycle. Actual duty cycle
will vary by up to 2% from ideal due to the type
of algorithm used to maintain sync-lock. This
algorithm also contributes to a slight variation in
period that is automatically corrected for every
four cycles. Typical timekeeping functions will
normally not be affected by either variation.
reset (pin 4)
This pin can optionally be used to reset the circuit
by applying a logic low level to it. While held low,
both outputs are placed in an open or tristate
condition. If unused, this pin should be left open
(as a pullup resistor is provided) or connected to
VDD.
VSS (pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
sync (pin 5)
The synchronizing reference is (optionally)
applied to this pin. Slowly varying sinusoidal
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface
mount type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP............................... ELM440P
200 mil SOIC..................................... ELM440SM
All rights reserved. Copyright ©1999 Elm Electronics.
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.
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ELM440DSB
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