STAR•TECH JOURNAL/SEPTEMBER 1982
10
A Regular Monthly Feature Technically Outlining a Newly Released Game
ATARI'S "KANGAROO"
By Joe Connor, Active Amusement, Philadelphia, PA
As can be seen, a large percentage of the video board is
made up of 4116 dynamic RAMs. A closer look at this
RAM (also used in Williams' and Taito's universal
systems) may be helpful.
4116 RAM -The4116 is a 16,384 x 1 dynamic
random access memory device. All inputs are fully
TTL compatible, as is the unlatched three-state output.
A dynamic RAM is one which must be "refreshed"
repeatedly in order to retain the stored data. In basic
terms, this RAM can be thought to have sixteen
thousand tiny little capacitors which will lose their
charge unless a control signal to the RAM is repeated
over and over again during operation. This refresh
operation must be performed at least every two
milliseconds to retain data. Strobing each of the 128
row addresses (AO through A6) with RAS cause all
bits in each row to be refreshed.
"Kangaroo" is Atari's latest video game and, like its
predecessor "Dig Dug", is not an original design, but
instead. is manufactured under license from Sun
Electronics Corporation. The game features I or 2
player action and is currently available in an upright
cabinet only. Game play can be classified as being of
the "Donkey Kong" genre with the player controlling
a boxing mother kangaroo that must hop and leap from
the bottom of the screen to the top to rescue her
kidnapped baby. The player must punch out monkeys
and avoid thrown fruit in an effort to reach the top.
There are four distinct rounds per skill level, with each
round becoming more difficult as it is completed. Like
some recent hits (Midway's "Pac-Man", Nintendo's
"Donkey Kong"), game play is designed to appeal to
the entire spectrum of game players - young and old,
male and female.
BOARD SET
While overall game design has been adapted to
conform to past Atari products ( especially "Dig
Dug"), the board set in "Kangaroo" has not. The
single logic board that we have all come to expect from
past Atari raster-scan games is not present; instead,
the board set consists of two boards, stacked one on
top of each other, interconnected by a 50-pin ribbon
cable. These boards physically resemble those found
in Centuri's "Phoenix".
CPU BOARD - The top board (CPU) is the
main board of this system and is made up of three
principle elements; the game CPU, the sound CPU,
and a custom 4-bit microprocessor. The game micro-
processor (IC15) can access 24K of program ROM
and 1 K of working RAM. Additional circuitry would include the address
decoders, and 1/0 section, and numerous buss drivers and tranceivers.
The sound section is controlled by a separate Z80 (IC34) which can
access its own 4K of ROM and IK of scratchpad RAM. This processor
dictates control over an AY-3-8910 sound generator (IC50), which
provides a filtered sound output to the audio amplifier (IC61).
The final element of the CPU board is a custom microprocessor(IC29).
This 4-bit microprocessor provides software security by creating software
loops which would be difficult to copy without access to this custom part.
This processor accesses data from a 2K E-PROM (IC28).
VIDEO BOARD - The bottom board of the "Kangaroo" board set
contains, as the name implies, all circuitry relating to displayed video
information. Principle sections of this board include sync and timing chains,
the picture ROMs, the playfield and motion object RAMs with address and
data multiplexirs to control them, and the video output circuitry. This board
is normally hidden from sight by the top board, but when exposed, reveals an
IC layout of incredible density. The printed circuit board measures
approximately 12" x 9" and is crammed with 142 chips! By comparison, an
Asteroid board measures 19" x 11.5" and contains "only" 119 chips. This
board also appears to be of three-level construction with a ground plane built
through the center, probably to help reduce noise problems from all the
dynamic RAMs.
BOARD HARDWARE
Video Board
CPU Board
Game Processor ( 1 }-Z80 Display PRO Ms ( 4)-2732
SoundProcessor(l}-Z80 Dynamic RAMs ( 32}-4116
Output Color Drivers
Custom Processor
(l}-74LSOO
(l}-MB8841
Working RAMs ( 4}-2114
Program PROMs (7}-2732
Ul·Pln Ceramic
Dual-In-Una Package
(Top View)
Vbb 1
D 2
w 3
RAS 4
AO 5
A2 6
Al 7
Vdd 8
AO-A6
CAS
D
Q
RAS
16
15
14
13
12
11
10
9
Pin Nomenclature
Address Inputs
W
Column Address Strobe *Vbb
Data Input
•vcc
Data Output
*Vdd
Row Address Strobe
Vss
Vss
CAS
Q
A6
A3
A4
A5
Vee
Write Enable
-5V Power Supply
5V Power Supply
12V Power Supply
OV Ground
THEORY OF OPERATION - Fourteen address bits are required to
decode 1 of 16,384 cell locations. Seven row-address bits are set up AA~s
AO thru A6 and latched onto the chip by the row-address strobe (
).
Then the seven column-address bits are set up on pins AO thru A6 and
latched onto the chip by the column-address strobe (iAS). All addresses
must be stable on or before the falling edges of RA and CAS. RAS is
similar to a chip eSable in that it activates the sense amplifiers as well as the
row decoder. CA is used as a chip select activating the column decoder and
the input and output buffers.
•Of special interest to the technician working on a game like "Kangaroo" is
that these RAMs run off of three supply voltages, +5, + 12, and -5. The
recommended operating conditions for this RAM specify a tolerance of
±10% for each voltage (i.e. +12 volts should be no lower than 10.8 or
higher than 13.2). Any technician working on Williams' "Defender" has
probably encountered logic boards with multiple failures of the 4116
RAMs. The symptom would usually be bad video and the smell of burning
flesh as you brush your hand across the RAMs. The cause of these failures is
generally accepted to be power supply breakdowns. Any board with triple
supply RAMs could fail in a similar manner, but it was especially noticeable
in "Defender'' because of the large number sold. There are many theories as
to which particular voltage failure causes massive RAM destruction but
probably the most widely believed is a failure in the -5 volts supply. The
power up conditions for this RAM specify that Vbb (pin 1, -5 volts) must be
applied to the device either before or at the same time as the other supplies
and removed last. Failure to observe this precaution will cause dissipation in
excess of the absolute maximum ratings due to internal forward bias
conditions. This also applies to system use, where failure of the Vbb supply
must immediately shut down the other supplies.