Play Meter

THE TEXTBOOK OF VIDEO GAME WGIC
S14 .95
III Pages , I 9 mustration'l
Have you ever wondered how video games
really work? After all, how do they get those
images on the TV screen and move them around
so realistically?
The Textbook Of Video Game Logic not
only describes how the video game computer it-
self works, but also the operation of all basic
digital logic devices. The book is primarily orien-
ted to video game designers and technicians, but
anybody interested either in video games or in
digital logic applications will find a great deal of
valuable material.
The first chapter deals with the operation of
common small scale digital integrated circuits
(the basic gates) and medium scale devices (flip-
flops, counters, shift registers, multiplexers, etc).
The logic symbol, schematic and truth table for
each device is carefully explained in simple, basic
terminology that requires no previous digital or
computer experience to fully understand the
material presented.
Once the reader has gained a basic under-
standing of digital circuitry and TV monitor op-
eration, the following chapters on video game
computer circuitry are easy to understand. The
next chapter deals with general video game ar-
chitecture, meaning the different techniques by
which a game can be r.reated.
Chapter 4 is a thorough discussion of video
game power supplies (and power supplies in gen-
eral). Using actual oscilloscope photographs, this
section graphically illustrates how raw AC power
is processed into a completely regulated DC
source.
Probably the most interesting section how-
ever is the chapter on creating images (chapter
7) . [mag s can be created by either of two tech-
niques : generated images and stored images. The
generated images are produced by individual cir-
cuits composed of small random logic elements,
however stored images are held in a special type
of semiconductor memory known as a ROM or
Read Only Memory . The ROM allows a game de-
signer to enter an image directly into the device.
This chapter explains not only how this is done,
but also how the image is then read out of the
ROM and displayed on the TV screen.
+~
+B.5V/
+5V-------------------------
FIGURE 1. 11 - 1 AND & NAND SYMBOLS
After dealing with all this basic information,
the book gets a lot more interesting. For you
TV terminal freaks, chapter 5 will be quite fas-
cinating since it goes into an in-depth explana-
tion of synchronization and timing circuitry. It
describes in detail the differences between inter-
laced and non-interlaced raster scans and precise-
ly how the image is synchronized with the elec-
tron beam so it is displayed in the right place.
FIGURE 7 .7 - 1 A DIODE MATRIX IMAGE Any"mpl e
Image such as the one above cln be stored In I diode ma o
tr ix - the '.rl'Ht form of read-only me mory . The mem o
or'V IS scanned and the dati read out by two sets of count·
ers. The vertical counter selects each hne of the Im.ge
while the horu:onl.1 one scans each pOint Iiong the 'mi .
A
I
B
y
V
~
II
LJ
Rl
R2
330n
330n
FIGURE 1.11 - 2 AND & NAND LOGIC
FIGURE 7 .9 - 1
Considerable time is spent showing exactly
how more complex devices such as counters are
built from the simpler digital building blocks
(gates).
Chapter 2 deals with the theory and opera-
tion of TV monitors . This is a basic explanation
of how the circuitry of the TV monitor gener-
ates the pattern of lines (the raster) on which are
displayed the various images. There is even a
nice little section describing how to tum any
regular TV into a TV monitor capable of taking
direct video input.
HORIZONTAL RETRACE
FIGURE 2.7 - 1 NDN ·INTERLACED RASTER SCAN
This 1ype of scan IS used 10 almost all video games SlnCI It
is a bit easier to implement than th e Interlaced 525 " 10'
variety used In TV broadcasting . Although onlv 262 Itnes
are scanned , the rHolUtion IS generallv adequate tor the
amount of Information neadlng to be displayed for •
video gam • .
PROGRAMMING A PROM The .. 'wo
photographs show a smgle fuse of a PROM before and
Iher programming . A speCial se t of pulses fed Into the
PROM 's outputs " blow " the addressed bi!.
FIGURE 5 .2 - 1 A CRYSTAL CONTROLLED OSCILL ·
ATOR
ThiS Simple OSCillator CirCUit 1$ used
In
almost
every Video gam. to generate the mast er tlmlllg Signal
known
~s
the CLOCK .
The final two chapters describe score and
paddle circuitry. Every video game must have
some sort of score circuit and this section shows
how numbers are placed on the TV screen and
changed as the player gains more points. The
paddle s ction illustrates how paddle images are
created by a special circuit and controlled by
turning a potentiometer on the game cabinet.
Successive chapters are concerned with how
images are generated and moved . Chapter 6 is
exclusively devoted to the subject of motion and
uses examples from various games to show how
the game designer controls the direction and vel-
ocity of a moving image .
TilE TE THOOK OF
i f)ubli hcd by Ku sh
Eleclroni s lllc.
IDEO
luff
IE LO
Ie
mu ment
60 Dillon Ave ., No. D Campbell, CA 95008 (408) 379-7180