O CIARCUIT

The Spectrum video circuitry is based around the LM1889N integrated circuit

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10. THE VID:

ISSUE 2 BOARD

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red-yellow) from the ULA, and produces a single colour output
more economic to use colour diflerence signals rather than separate

The colour is mixed with the incoming composite video syne. and

and blue signals. Onty two sets of circuitry are reguired instead of three

produced by National Semiconductor. The full circuit diagram is illustrated in fig.
9a. This integrated circuit accepts two colour difierence signals (U s bl

yellow, V
signal. His
red, green
for RGB.

posite colour video signal. AHer
9 TR2, the video signal is fed into

information to be dis

luminance (Y from the ULA) to produce the com
being buffered by an ernitter follower circuit usin

zi tij

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pliication of

yellow signals. By changing these adjustments you can
guality or the grey scale. See the next chapter for details on

vary the output colour
how to accomplish this.

played on an
because some

ty of display obtained

by using a colour monitor with a

The two adjustment resistors VR1 and VR2 alter the relative am

colour monitors reguire these inputs. The rather poor guali
the red-yellow and blue-

wilh a television can however be improved upon
composite video input.

the video modulator. This enables the video
— ordinary television. H is unfortunate that RGB video was not used,

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PLATE 9 —PHOTO OF MAIN SPECTRUM BOARD
OUTLINED VIDEO CIRCUIT