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MICRO
PROCESSOR
GBPB — GameBoy
Prototyping Board
A development aid for the GameBoy
Design by L. Lemmens
In previous editions we
proved beyond doubt
that the Nintendo
GameBoy is perfectly
suitable for more serious
tasks than playing games.
The sampling oscilloscope
described in the October
and November 2000
issues was a prime
example. In the
December 2000 issue,
we published a follow-up
article on GameBoy
Development Tools. This
month it’s time to offer
help in the hardware
department.
42
Elektor Electronics
1/2001
MICRO
PROCESSOR
+5V
RD
DX
1
2
3
15
+5V
0
1
2
3
4
5
6
7
0
G
0
7
14
+5V
A13
13
2
WR
K1
12
IC2
Game Boy
11
ECLK
WR
74HC138
32
31
A14
4
5
10
+5V
A000
9
ECLK
&
30
A15
6
7
WR
RD
29
28
RD
+5V
RAMCS
27
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A0
+5V
16
26
C1
C2
A1
IC2
25
+5V
A2
100n
100n
24
8
A3
K2
1
VPP
28
23
A4
K3
22
1
2
A5
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
A15
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9
A10
A11
A12
A13
A14
10
A0
21
3
4
A6
9
A1
20
5
6
A0
K4
A7
8
A2
19
A1
7
8
A2
11
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
A8
D0
7
A3
18
17
16
15
14
13
12
A3
9
10
A4
12
IC1
A9
D1
6
A4
A5
11
12
A6
13
A10
A11
A12
A13
A14
A15
D2
5
A5
A7
13
14
A8
15
D3
4
EPROM
A6
A9
15
16
A10
16
D4
3
A7
A11
17
18
A12
17
D5
25
27C256
A8
A13
19
20
A14
18
D6
24
A9
A15
21
22
D0
19
D7
21
A10
11
D0
D1
D2
D3
D4
D5
D6
D7
D1
23
24
D2
D0
23
A11
10
D3
25
26
D4
D1
2
A12
9
8
7
6
5
4
3
2
1
D5
27
28
D6
D2
D3
D4
D5
D6
D7
26
A13
D7
29
30
27
A14
31
32
33
34
CS
OE
20
14
22
A15
RESET
AUDIOIN
GND
000151 - 11
Figure 1. Circuit diagram of the GameBoy Prototyping Board (GBPB)
A helper board
In the December 2000 issue of
Elek-
tor Electronics
we supplied pointers
to a variety of GameBoy emulators
that allow software for this
extremely popular ‘games console’ to
be tested on a PC. Emulators are fine
tools for projects consisting of soft-
ware only. However, the moment
extra hardware has to be linked to
the GameBoy, two problems occur:
the connector for the (game) car-
tridge is a Nintendo proprietary
design and to make matters worse it
is hidden deep in the GameBoy case.
These problems with the card
edge connector do not appear when
a PCB is designed and etched
straight away for the prototype of
the circuit you have in mind. Still,
because a large part of the cartridge
board is hidden by the GameBoy
case, it will be hard, if not impossi-
ble, to do any measurements on the
new board. Sure, it is possible to
open the GameBoy case by removing
the screws that hold the rear panel.
That way you have access to the car-
tridge board, at least for measure-
ments. However, opening the Game-
Boy case is a far cry from the ideal
solution because the screws are dif-
ficult to remove with an ordinary
screwdriver. Moreover, opening the
GameBoy case voids the product
warranty you may have, and without
the rear panel there is no battery
case! The most annoying problem is,
however, that the prototype is at the
rear side of the GameBoy, while the
display and controls are located on
the front (now who did that
design?).
All of the problems mentioned above are
avoided by our prototyping board of which
the circuit diagram is shown in
Figure 1
, and
the PCB design, in
Figure 2
.
Any components on the prototyping board
will be visible and accessible when the
GameBoy lies horizontally on your desk. This
allows measurements to be carried out on the
prototype hardware while the GameBoy dis-
play and buttons are accessible at the same
time.
The cartridge connector is part of the PCB,
and its connections are linked to a standard
34-way boxheader. In many cases, this is suf-
ficient, because it is then easy to connect
your own (experimental) board to the Game-
Boy via a length of standard flatcable. The
order of the connections is given on
Table 1
.
Note that the boxheader has 34 pins while
1/2001
Elektor Electronics
43
MICRO
PROCESSOR
A15
A14
A13
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
A0
D7
D6
D5
D4
D3
D2
D1
D0
C1
IC1
C2
K4
IC2
A000
K2
/RD /WR
ECLK
/WR /RD
+5V
K3
000151-1
Figure 2. PCB design.
COMPONENTS LIST
Capacitors:
C1,C2 = 100nF
the GameBoy cartridge connector
has only 32. The simple reason for
choosing a 34-way boxheader is that
a 32-way version does not exist.
Extension cards like the one
described here usually have a proto-
typing area where additional com-
ponents may be fitted to test a par-
ticular circuit you have in mind. Such
a prototyping area has been pur-
posely omitted here. The essential
point in this case is to make the spe-
cial cartridge connector and the
extension part accessible well out-
side the GameBoy case. Veroboard is
cheap and widely available from
local electronics shops (or by mail
order), and easy to connect via a
piece of flatcable. What’s more,
despite accurate soldering and des-
oldering, prototyping board will not
last long when used frequently.
Semiconductors:
IC1 = socket for 27C256
IC2 = 74HC138
Miscellaneous:
(K1 = card edge connector on board)
K2 = 34-way boxheader
K3 = 16-way SIL-header
K4 = 8-way SIL-header
PCB, order code
000151-1
(see Readers
Services page)
Options
Connectors K3 and K4 are initially
intended to facilitate measurements
on the data and address bus. You’ll
44
Elektor Electronics
1/2001
MICRO
PROCESSOR
find the data and address lines
neatly arranged on these contact
strips. Of course, the lines may be
used for external connections. Simi-
lar cons
ide
r
ation
s apply to the PCB
pins for RD, WR, ECLK and the two
supply connections +5 V and GND.
The latter pins should only be
used for supply voltage measure-
ments, or for powering an external
circuit. They must
never
be used to
power the GameBoy or the hardware
on the extension card.
Any cartridge should contain a
piece of software in ROM that allows
the GameBoy to start up. That’s why
a socket for the 27C256 EPROM is
provided on the extension board.
The memory may of course also be
located on the board connected to
K2. In that case, IC1 should not be
fitted on the extension board.
An EPROM emulator like the one
described elsewhere in this issue is
conveniently coupled to the socket
for IC1. Such a configuration is very
useful and handy when you are into
developing software for the Game-
Boy — write and assemble the
source code on the PC, load the
object code in the emulator using a
HEX file transmitted via the serial
port, and finally test the program on
the GameBoy. Arguably, this is a
much faster process than erasing
and reprogramming an EPROM
after every modification made to the
program.
The circuit includes a 74HC138
(IC2) which allows two selection
lines to be decoded for controlling
external hardware. Pins 9 and 10 of
the ‘138 carry the active-Low read
and write signals respectively for
address A000. For ease of connec-
tion, these signals are brought out to
PCB pins.
cause problems. You should, however, con-
sider how the board will be used, that is, with
the EPROM mounted on it or with the mem-
ory device located on the external board. In
many cases, boxheader K2 will suffice. If you
are only into developing and testing software
for the GameBoy, it is sufficient to fit the
EPROM socket only.
(000151-1)
Construction
Before the soldering iron is powered
up, you should check if the board fits
in the GameBoy. Note that the nor-
mal thickness of the cartridge case
plus board should be about 2.5 mm
to ensure proper contact with the
GameBoy cartridge connector. Here,
we only employ the PCB (i.e., no car-
tridge case), and that is why the
PCBs supplied ready-made through
our Readers Services have been pro-
duced with a special thickness. If
you want to make your own board
from the layout shown in Figure 2,
but do not have PCB material of the
right thickness, a thinner size may
be employed. Strips of cardboard or
plastic may be glued on to the bot-
tom side of the board to achieve the
same effect. This should be done
with care and precision — if the con-
nector is too thin, the contact with
the GameBoy will be unreliable ore
even totally absent. A too thick con-
nector, on the other hand, means a
serious risk of damaging the Game-
Boy connector beyond repair.
Populating the board will not
Table 1.
Connections on
the extension
board.
K2 pin # . . . . . . . . . . . signal
1 . . . . . . . . . . . . . . . . . . . VCC
2 . . . . . . . . . . . . . . . . . . .
ECL
K
3 . . . . . . . . . . . . . . . . . . .
WR
4 . . . . . . . . . . . . . . . . . . .
RD
5 . . . . . . . . . . . . . . . . . . . RAMCS
6 - 21 . . . . . . . . . . . . . . . A0 - A15
22 - 29 . . . . . . . . . . . . . .
D0 - D
7
30 . . . . . . . . . . . . . . . . . . RESET
31 . . . . . . . . . . . . . . . . . . Audio input
32 . . . . . . . . . . . . . . . . . . GND
33, 34 . . . . . . . . . . . . . . . not connected
K3 pin # . . . . . . . . . . . signal
1 - 15 . . . . . . . . . . . . . . . A0 - A15
K4 pin # . . . . . . . . . . . signal
1 - 8 . . . . . . . . . . . . . . . . D0 - D7
1/2001
Elektor Electronics
45
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