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*
13)
firing
*
14)
firing
[enemy]
*
15)
target
*
16) fuel
*
SELF-TEST
END
Due to the
striking isometric perspective used
in
ZAXXON,
memory
requirements for background generation are significant.
On
Assy
IC
Board
B
(834-0211), EPROM's 4-15 contain
a
total
of 672K bits of video character,
positioning, color, and timing information.
Background generation accessible
memory
is
provided
by TTL Isoplaner RANs U42, U64 {Zone 6-B, Sht. 8, Assy.
IC Bd. B),
and U46 (Zone 2-D,
Sht. 6,
Assy.
IC Bd. B), in
addition
to the
1024
X
4 bit
RAMs U17 and U36.
Composite synchronization
is
taken from pin-4
of Ull (Zone 2-C, Sht.
7, Bd. B)
applied
to
p1n-5 of U93 (Zone 7-A, Sht.
13,
Assy. IC Bd. A),
selectably polarized
by switch SW4 and put on
pin-20
of P5,
for input to the monitor,
in
addition
to
W, 19,
and
X.
180° video FLIP for
cocktail models
is
latched into the data
bus by SWl
position
8
through
U87
(Zone 3-B, Sht.
13,
Assy.
IC Bd. A).
Just
as
the
microprocessor Z80A
is
the heart of the game computer,
so too
is
the
825bAC-5
(U23, Zone 8-C. Sht. 12, Assy. IC Bd.
A)
the
center
of
activity
in
the
Sound area.
Called
a
Sound Generator, U23 interfaces data
and
address
bus,
enabling specific sound processing circuits.
These circuits
consist of individual sounds
for Player Ship Flying Sounds, Homing Missile,
Base
Missile, Barrier, Robot, Small-explosion, Large-explosion,
Laser, Enemy
Shot, Target, and Fuel.
Those complete sounds not originating within the
8255A, are enabled
by
the Sound
Generator
Chip through
a
device called
a
Quad
Switch/Driver
(4015B) U17.
Ull and VRl (Volume Control, found on the Assy.
A
ie
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