Play Meter

(continued from page SS)
are desirable, especiall y for the
professional technician but they are
not essential. W hat is absolutely
essential is the knowledge of why
the video game computer is con-
structed the way it is and how the
specific devices and circuits actually
operate .
An excellent source for the an-
swers to these questions is the
Video Game Data Library's Data
Books and Computer Service Man-
uals. Each manual is an exhaustive
analysis of a particular game and
contains a great amount of informa-
tion available from no other source .
INTRODUCTION
The prime factor influencing the
success of video games is the fact
that players are fascinated by
watching and being able to move
glowing images around the cathode
ray tube of the TV monitor. This
being true, techniques for gener-
ating images are one of the most
important single design considera-
tions for successful games, so a
great deal of research has been
done to discover new and more
efficient ways to generate and store
image information.
The importance of display tech-
niques has led to a number of
interesting innovations and clever
circuits, however most of the basic
techniques have not been develop-
ed specifically for video games.
Rather, these methods are based in
other fields of digital electronics
such as semiconductor memories
and computer terminals where the
display of characters is of the
utmost importance and a great deal
of research has led to many of the
techniques we see today in video
games. Although the basic con -
cepts as applied to video games
were not originated by game de-
signers, their application in games
has resulted in some highly original
and interesting circuit designs.
Early games were, of course, the
simplest and the techniques used
were the most basic . In fact, the
earliest games depended very little
on sophisticated display techniques;
they were successful merely be-
cause of the newness of the craze .
However, even these games needed
some display and engineers came
up with a number of simple, but
interesting techniques for genera -
ting basic images such as paddles
and score numerals . But as players
became a little jaded , designers
began to search for ways to
generate more complex images and
it quickly became obvious that the
FIGUR E 3 : A COMPL ETE WINDOW
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12
13
14
15
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CLOCK
0,----'
0.:- - - - - - - '
0 0- - - - - - - - - - - - - '
FIGURE 4 : COUN TE R OU TP UT WAV EFORM S
NOllce tha t th e ou tp ut o f eac h successive "aV' changes
at o nt ·h, lf the ,. te of th e prevIOus one .
34
I
old methods would be too unwieldly
for the greater number of more
detailed shapes required .
GENERATED VS. STORED
DISPLAYS
The techniques pioneered by the
. first games are still in use even in
state-of-the-art games, however
their importance has drastically
decreased . These techniques all
centered around the generated dis-
play concept where a circuit using
basic components such as gates
and flip -flops produced an algorithm
which resulted in a particular shape
on the CRT. To create images using
this technique, sync submultiples are
combined in various ways to pro-
duce geometrically oriented shapes.
10
COUNT
To f orm
comptete w indow . the Ire. must be defined on I II four
sid. s by comb ining both the horizontal Ind ..,.rt ical w in-
dows.
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While this technique was eminently
successful , its limitations quickly
became apparent for not only does
this technique require many sepa-
rate chips and a considerable a-
mount of PCB real estate, but is also
quite limited in the amount of detail
which can be conveniently pro-
duced and the flexibility with which
a particular shape can be effected .
So designers began to explore
ways with which they could pro-
duce specific and intricate shapes
they had in mind while keeping
circuits simple and minimizing the
total number of ICs required for a
particular game theme. The only
other digital technique which ap-
peared applicable was that of stored
displays which depend on some sort
of memory to retain the information
needed to generate the images . The
essential difference between th is
technique and the generated display
is that stored information is read out
only when needed -- it is not
constantly being produced .
The first games using stored
displays depended on the diode
matrix to hold the information .
Although the diode matrix cannot
conveniently hold a great deal of
data , it does allow the designer a
good measure of flexibility insofar as
he can easily plot out and execute
the shape he has in mind. But more
important is the fact that the diode
matrix can be built with ordinary
parts lying around the lab and does
not require the hassle and expense
of programming a real memory . In
the days of the early video games,
only one type of read -only memory
was available and this mask -
programmed ROM required a con-
siderable investment of money to
pay for the initial mask charge to
enter the specific data . This was
pretty scary to designers, so they
avoided ROMs like the plague .
But today , there are many new
varieties of ROMs available which a
designer can program in his own
lab. This allows him to check for
mistakes and have the results he
needs inexpensively and quickly .
When a final shape has been
decided upon , he can then produce
a limited run of PROMs so prototype
games can be manufactured and
tested to see if the design will be
successful. If the prototype results
are en couraging , the manufacturer
will feel justified in having a mask
cut so that a large number of
relatively inexpensive memories can