Play Meter

be programmed with his data.
The proliferation of integrated
semiconductor memories has led to
an entirely new video game archi-
tecture . Many, if not most, of
today's games are virtually built
around the ROMs they contain and
it is not unusual to find that the
ROM in a game contains all the
object shapes, score numerals, mo-
tion codes and other instructions
and data the computer might need.
BUILDING A GENERATED
DISPLAY
Sync submultiples can be gated
together in an endless variety of
ways to generate many types of
images ranging from the very simple
to more sophisticated shapes which
appear quite complex. If the display
requirements are relatively basic,
SSI components are normally used
but often more complex images can
be derived using MSI devides such
as counters and magnitude compar-
ators without increasing (or maybe
even decreasing) the total number
of ICs required for the particular
image . All generated display tech-
niques depend heavily on the use of
windows to specify certain areas of
the CRT .
THE WINDOW CONCEPT
The term window is one which
has been coined to describe a
selected area of the CRT. A window
is created by using the appropriate
sync submultiples to define the
limits or boundaries of the desired
area.
Figure 1 shows how the subultiple
64H appears when displayed on the
CRT with a video probe . As always,
the dark areas represent the LO time
periods of the signal and the light
areas occur only when 64H is Hi.
The submultiples can be ex -
amined by a number of instruments.
Unfortunately, the logic probe will
reveal Hi , Lo and Pulsing where the
only noticeable difference between
outputs is a progressive decrease in
symmetry further down the line.
However a scope will reveal wave-
forms which correspond exactly to
the characterizations in Figure 4.
This brings us to another instru -
ment which is very useful in probing ·
these kinds of circuits : the video
probe. A video probe is nothing
more than a 4.7K resistor attached
to a jumper which has an IC clip on
one end and a test prod on the
other. The resistor can be hidden in
either the prod or the clip to keep it
out of the way .
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The video probe is used primarily
for examining video signals but it
can also be used as a sound probe .
When used to probe for noise, the
clip is atached to the input of the
audio amplifier and the test prod can
then be used to hear any signal fast
enough to produce a tone . Gener-
ally, a noise probe is used to check
sound circuits, but it can also be
used to " hear" sync chains working
because--as you move down the
chain --the tones become success-
ively lower at each division .
But the most valuable use of the
video probe is in examining video
signals used in the developement of
more processed signals where the
developemental signals you need to
check are not visible on the monitor
CRT. But, if you connect the probe
clip to the negative side of the
coupling capacitor found in the
video summation section , the signal
present at any node you touch with
the prod will be injected directly into
the video output line . If the ex-
amined signal is of a video nature,
meaning it is neither too fast nor too
slow, it will be displayed as an
identifiable shape on the monitor
CRT.