V1, V2, and V3 (pins 7, 6, and 5)

These are the digital to analog converter’s logic

level output signals. When combined through a

few appropriate resistors (shown in the Example

Application section), a standard 1Vp-p NTSC

video signal is created. Output levels during the

signal phases are as follows:

V2

Sync

Blanking

20% White

40% White

60% White

100% White

L

L

L

H

L

V3

L

L

H

L

H

H

H

V1

L

H

L

H

H

H

Signal Phase

These signal levels and how they relate to the

actual video waveforms are shown pictorially in

the Example Applications section.

Circuit common is connected to this pin. This

should be the most negative point in the circuit.

ELM304

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Pin Descriptions

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............................... ELM304P

208 mil SOIC..................................... ELM304SM

2 of 6

All rights reserved. Copyright1999 and 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.

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 3.579545 MHz NTSC television colourburst

crystal is connected between these two pins.

Crystal loading capacitors (typically about 27pF)

will also normally be connected between each of

these pins and Vss.

This frequency was chosen as the crystal should

be readily available, and inexpensive. This circuit

is not able to use the crystal output to generate

colour bars.

Mode (pin 4)

The ELM304 can be selected to operate in one of

two modes depending on the logic level at this

pin. When at a high level, the generated raster

will be 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/gray levels.

ELM304DSC

Ordering Information