ELM440

Elm Electronics – Circuits for the Hobbyist

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Pin Descriptions

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

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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.

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.

XT1 (pin 2) and XT2 (pin 3)

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.

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

sync (pin 5)

The

synchronizing

reference

is

(optionally)

applied to this pin. Slowly varying sinusoidal

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

1Hz (pin 6)

The output on this pin is a 1Hz signal of

nominally 50% duty cycle.

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.

Circuit common is connected to this pin. This is

the most negative point in the circuit.

ELM440DSB