ELM ELM304SM, ELM304P Datasheet
ELM304
1234876
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NTSC Video Generator
Description
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Features
The ELM304 is a low-cost NTSC video signal
generator in an 8 pin package. Requiring only an
external crystal and a few passive components, this
circuit produces a stable raster that is suitable for a
variety of video applications.
The ELM304 can be ‘programmed’ to generate
either a solid white raster or a four-level gray scale
pattern simply by changing the logic level at the
mode input pin. A supplied internal pullup resistor
further simplifies the circuitry when interfacing to
mechanical switches.
Although originally designed to provide a stable
video input signal for use while recording audio on
video cassette recorders, this circuit can also be
used for many other instructional and test purposes.
The low power consumption and small size of the
circuit also makes it ideal for battery-powered
applications.
Applications
• Video Source for Video Cassette Recorders
• Classroom Instructional Aid
• Test Bench Video Generator
• Low power CMOS design - typically 1mA at 5V
• Wide supply range - 3.0 to 5.5 volt operation
• Uses a standard 3.58MHz crystal
• Generates both solid and bar type patterns
• No external amplifier required
• Standard 1V p-p NTSC sync negative output
• Requires no adjustments
Connection Diagram
PDIP and SOIC
(top view)
VDD VSS
V1XT1
XT2
Mode
V2
V3
Block Diagram
V1
XT1
XT2
ELM304DSB
Master
Oscillator
Mode
Pattern
Generator
VDD
Output
Matrix
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V2
V3
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ELM304
Pin Descriptions
VDD (pin 1)
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.
Mode (pin 4)
The ELM304 can be selected to operate in one of
two modes depending on the logic level on this
pin. When at a high level (or open-circuited), the
generated raster is solid white in colour. If this pin
is held at a low level, the circuit will generate a
four-level pattern of typically 100%, 60%, 40%
and 20% white.
V3, V2, and V1 (pins 5, 6, and 7)
These are the digital to analog converter’s logic
level output signals. When combined through a
few appropriate resistors (see the example
application section), a standard 1Vp-p NTSC
video signal is created. Output levels during the
signal phases are as follows:
Signal Phase
Sync
Blanking
20% White
40% White
60% White
100% White
V3 V2 V1
L L L
L L H
H L L
L H H
H L H
H H H
VSS (pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
Ordering Information
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.
ELM304DSB
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............................... ELM304P 200 mil SOIC.....................................ELM304SM
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