A Look at the Gameboy DMG

17 Jun 2020 | 20 minutes to read

The original Gameboy was an 8-bit handheld console created by Nintendo. It was technically their second handheld console, the first being the Game & Watch series. The same team that developed the Game & Watch games also worked on development of the Gameboy, which went on sale on April 21, 1989 in Japan and July 31 in North America. It was originally sold for only $89.95, about $185.99 in 2020 dollars. It was Nintendo’s primary handheld console until the release of the Gameboy Color in 1998.

Before the Color, the Gameboy Pocket and Gameboy Light were released but they weren’t hugely different than the DMG, more like minor revisions than a new handheld. Despite the color being release, the Gameboy DMG (Dot Matrix Game) continued to be sold until 2003, after the release of the Gameboy Advance.

The DMG had a total of 6 launch titles, though some were only released in specific regions:

Title	JP	NA	EU
Alleyway	✅	✅	✅
Baseball	✅	✅	✅
Super Mario Land	✅	✅	✅
Tennis	❌	✅	❌
Tetris	❌	✅	✅
Yakuman	✅	❌	❌

By the end of it’s life, around 1,056 different games made for the system. The last game released in Japan was Shikakei Atama o Kore Kusuru: Kanji no Tatsujin on March 30, 2001. The last game released for both North America and Europe was Pokemon Yellow on October 19, 1999 and June 16, 2000 respectively.

Now let’s talk about this one specifically.

Case

The faceplate of the case

Compared to the plastic on the inside, it’s a little yellowed but that’s to be expected with how old it is. I hope to eventually get my hands on some retro-bright and restore it back to it’s original grey. I am especially happy with this Gameboy because it still has both the battery cover and the communication port cover.

Front

The screen takes up the largest part of the front, consisting of the screen itself and a plastic cover on top. Along the top of the plastic cover is the text DOT MATRIX WITH STEREO SOUND. Just below the screen the Gameboy proclaims it’s name to the world, with the text Nintendo GAME BOY TM. Just to the left of the screen is a small red LED that shows when power is on. It is simply labelled as BATTERY. It’s useful for figuring out if you need to fix the contrast of the screen, get new batteries or have a deeper issue as in my case…

Below that is the buttons and speaker grill. On the left is the D-Pad molded from black, which has a more mushy feel than later Gameboy handhelds. It has a divot in the center and two slightly raised sections in each direction, which you can see if you look closely. There are also small arrows in each direction molded on the case.

On the right is the A and B buttons, with the labeling on the case instead of being molded into the buttons like in later Gameboys. These buttons are also molded from hard plastic, though in a dark red or maroon like color.

The start and select buttons are both molded from a silicon-like material, and are even mushier than the D-Pad. One thing to notice is that they are angled, not parallel with the bottom of the case. To me, it makes it feel more slick and futuristic. The labels for the buttons are printed on the case, in the same direction as the A and B buttons, thought at a smaller font size.

Finally, the speaker grill is in the bottom right, outputting mono sound. It has 6 “slots” for sound to come out of, but only 5 of them have holes cut through the case.

Back

Back of the case with the battery door removed

Serial #: G06184423

Back text

MODEL NO.  DMG-01
©1989 Nintendo
RATING : DC 6V 0.7W
BATTERY : SUM-3(AAa,R6)X4
PAT. PEND. MADE IN JAPAN
Complies with the limits for a Class B computing
device pursuant to Subpart J of Part 15 of FCC Rules.

The back of the case is much simpler than the front, but you’ll definitely spend more time staring at the front than the back anyway so it doesn’t matter too much. Cartridges are loaded from the top, with the label facing out. When switched on, the cartridge is held in place by a small tab on the on/off switch.

Below that slot is the “battery bay”, which holds 4 AA batteries. A cover goes over the batteries, holding them in place. It is held by a little clip at the top and two legs at the bottom of the plastic.

To open up the case, there’s 4 screws on the outside and 2 inside the battery bay that need to be removed.

Edges

Top of the case

On the top of the case is the On/Off switch. To turn the console on, you move it toward the middle. When you turn it on, the button has a bit of plastic sticking out that holds the cartridge in the slot. This stops you from removing a cartridge while it is on. This “feature” was later removed from later Gameboys, I think when designing the original Gameboy they were worried that people would pull the cartridge out at the wrong time and corrupt the save data for whatever they were playing.

Right side of the case

Text: VOL ◢, EXT. CONNECTOR

On the right side, there is the communication port and volume knob. The communication port is a 6-pin plug that allows one to connect to other Gameboys over a serial interface. It had a variety of different modes, including a “Normal” mode for 1 to 1 connections, a “Multi-Play” mode for 1 to 1-4 connections where each had the same game, and a “Multi-Boot” mode. I most often used it for trading Pokemon, and not much else.

Left side of the case

Text: CONTRAST, USE ONLY DMG-03.-05, ⭪ DC 6V

The left side has the contrast knob and a jack to plug in external power. The knob allows you to adjust the contrast of the screen, which is extremely useful as it can take some tuning to get the screen to look right. It is about a third of the thickness of the volume knob. You have to fight against the ambient light around you, and as you play more and the battery drains it’ll start getting fainter. There are mods to install a fancy backlit screen, but that’s a mod for a different day.

The plug is intended to be used with the rechargeable battery pack, which would plug in via a cable. It was able to power the Gameboy on its own, and somewhat fixed the battery issue.

Case Booty

On the bottom of the case is the headphone jack. This allows headphones to be plugged in, letting you enjoy that sweet 8-bit stereo sound. I think it is ironic that the headphone jack was included on the original Gameboy, but not on the Gameboy Advance SP, which was made 14 years later.

The Insides

Two halves of the Gameboy, connected by a ribbon

To open the case, you must remove 6 screws: 4 on back and 2 underneath the batteries. Once those are removed, the case opens up into two sections connected by a ribbon cable, pivoting at the top. The front section contains the I/O inputs, speaker and screen hardware. The back section contains the main logic board, along with a power converter board and headphone jack board connected by wires to the logic board.

Screen and I/O PCB

The fronts of the screen PCB

Most of the heavily lifting is done on the logic board so the front PCB is pretty simple, with lots of blank PCB space. It’s attached to the front case piece with 10 screws, much more than the other PCB. They are spaced carefully around the buttons and screen to try and provide the most support. This PCB needs to withstand the pressure of the player pressing buttons, so the screws makes sure nothing warps or breaks in ways it shouldn’t.

The screen is a Sharp LH5028 160px x 144px monochrome LCD screen, capable of displaying 4 shades (2 bits worth) of green. The datasheet for the original screen can be found here. It rests on the PCB held in place by 3 clips part of the plastic screen housing. The screen contains two ICs that control drawing the X and Y axis. You can see the X axis chip in the image above, labeled 004. The ribbon for the X axis chip is held to the PCB by two small screws and a bar that is soldered across to hold it in place.

The front of the screen is glass, but is protected from damage and fingerprints by a plastic cover that attaches to the front of the case. When the plastic screen is inevitably scratched, it is easy to swap it out without having to worry about the damage being permanent. Because of their age and it’s effect on glue, many Gameboys have lost this screen. Luckily, it’s very easy to pick up a pack of 4 on eBay for cheap that look brand new.

The screen is pretty bulky and “meh” compared to modern screens. It requires the user to tune the contrast via a dial on the side. To make matters worse, as the batteries lose energy, the screen will also start to dim forcing one to adjust it every so often. One common modification is to swap out the screen with a modern, backlit screen. In addition to just looking better and being able to play in the sun, new screens can display 4 shades of grey instead of the original olive green.

I/O PCB, pads and buttons

The directional and A+B buttons are made of hard plastic, while the select and start are just soft buttons made of silicon. On the PCB, the D-Pad has two contact pads for each direction, while all other buttons have 4 to capture button presses reliably. The buttons are restored to their original position using silicon pads that go between the plastic button and the PCB, similar to a rubber dome keyboard. The D-Pad pivots directly on the PCB, which over time wears a spot which luckily doesn’t rest on any contacts or lines.

Back of the screen PCB while mounted in the case

The back of the PCB is stamped with the text 005.22, which matches number stamped on the other PCB’s heat sink. This means that we have a system with original matching boards that haven’t been swapped out, and are most likely the same that were installed in the case when it was originally manufactured.

This PCB is very well labeled, with each screw hole being clearly circled and each component labeled. At the bottom right on the back there is a circled letter Z. There is also an extra hole, which is very clearly marked to not have a screw inserted. There are also 3 simple spring type connectors that ground it to the logic board labeled E1, E2, and E3. When installed in the case, they make contact with 3 ground points on the logic board. to ensure that the front board has access to a solid ground, instead of trying to only use the ribbon cable. The board includes hole cutouts for the larger capacitors, and space for the speaker and audio jack to slot in between the pcb and the case.

One interesting thing about the board is the use of jumper wires, labeled using the format J#. Instead of using loose wires, there are specific cutouts in the ground layer of the PCB for the jumper to rest as to not cause shorts etc. They act as a third PCB layer; this board only has traces on the front and back, with nothing sandwiched in the middle.

The speaker is a simple 8Ω one, labeled 2P22a 8Ω JPN 04359. It connects to the board via two wires that wrap their way around the speaker to the board. It is directly connected to the audio amp present on the logic board via the ribbon cable.

The Logic Board

Logic board mounted in the case, showing all 3 boards

Logic board and attached daughter boards

The back of the case has 3 separate PCBs nestled inside of it:

Logic board
DV converter daughter board
Headphone port daughter board

The power and headphone boards are each separately connected to the logic board via 4 wires that attach to the bottom and side. At both ends of the wires theres a small piece of plastic melted on that keeps the ends correctly spaced apart for attaching to the boards when being soldered by hand.

This board is attached to the case back directly with only two screws, though the four external screws also hold it in place. The front of the board is where the majority of components are attached. The back contains traces, the ribbon connector, and a copper pad. The copper pad lines up with the chips on the front, and probably acts as heat sink. This is also where 005.22 is stamped, matching the stamp on the screen board. On my PCB, there is also a single fingerprint on the copper, probably from the person soldering the final parts on the board.

When mounted, the board has a good air gap between the chips and the back of the cartridge slot. There is no heat sink directly on the chips, but the air gap paired with a metal plate attached to the cartridge slot on the case help dissipate heat and give the case a bit more strength.

One of the first thing I noticed with this board was the how it smells like an old PCB, similar to an old Commodore or Atari 400. It looks as if most components on the board were attached using automated assembly lines, but some look like they were soldered by hand, due to some solder flux remaining on the board:

Copper heat shield
Audio and power board connections
Power switch
Power jack
Battery terminals
Volume knob
Communication port
Ribbon connector
Cartridge slot

The PCB is very square, measuring and 3 sides of the board have “rough edges”, meaning they were connected to each other in columns two PCBs wide when the PCB’s were being printed and assembled.

Closeup of main chips

There are 4 chips and a crystal mounted:

ID	Purpose	Chip Label	Board Label	Manufacturer
U1	Processor	DMG-CPU B © 1989 Nintendo Japan 9017 W	DMG CPU	Sharp
U2	64Kb VRAM	LH5264TN-L Sharp Japan 9017 1 Y	64K SRAM	Sharp
U3	64Kb SRAM	LH5264TN-L Sharp Japan 9017 1 Y	64K S-RAM	Sharp
U4	Audio amp	DMG-AMP IR3R40 9016 A	AMP	Sharp
X1	Crystal	D419C0	4.194304MHz	Daishinku

DMG Processor

The DMG does most of the heavy lifting, it is directly connected to most things on the board, including the VRAM, SRAM, cartridge socket, audio amp, I/O buttons, front screen, and external link port. It is a sort of hybrid of the Intel 8080 and Zilog Z80 processors, a Sharp LR35902. It adopts the instruction syntax from the Zilog, but much of the instruction set from the 8080. The DMG also adopted a single address space and didn’t contain extended addressing modes beyond 8-bits. It also meant that instead of having special instructions to access I/O input, it read their states from special places of mapped memory. More can be found here about their similarities and differences: https://gbdev.gg8.se/wiki/articles/CPU_Comparision_with_Z80.

VRAM

The video RAM chip is down and to the right from DMG chip. It is connected via some address lines, some data lines, and read/write latches. When writing data to the screen, the DMG will access this memory and send it to the screen, with the data routing back through the DMG chip to the screen. As it reads and sends pixel data, the DMG will also manage the screen itself, including clock signal, horizontal sync and vertical sync.

SRAM

The SRAM is located directly to the right of the DMG. It is the working RAM for use by the game. It is connected in a similar way as the VRAM, just to it’s own set of pins on the DMG processor.

Cartridge Slot

The cartridge slot is connected to many of the same pins as the SRAM. The DMG choosing which device to operate on by setting either the write or read pin for the device. This ensures that the DMG doesn’t accidentally attempt to read from both at the same time, which would surely result in garbage data being read or possibly an attempted double write of some sort.

Audio Amp

The audio amp manages the audio output. It is connected to the DMG chip by two lines, carrying the left and right audio. Volume knob is on other side of board, and is connected to the same two audio lines. This means that the volume knob adjusts the volume before it enters the audio amp chip.

I/O

I/O is read via 6 pins, 4 input and 2 output.

Diagram of the I/O circuit

The P14 and P15 pins are outputs, and P10, P11, P12, and P13 are inputs. Between the output pins and each button is a diode, which ensures current doesn’t leak.

To read the buttons, the DMG will first set one of the output pins high and read each of the input pins. If both P14 and P15 are high, the DMG would be unable to tell if the D-Pad was being pressed or one of the other buttons. When fetching the states of the A, B, Select and Start buttons it will set P15 high, and to read the D-Pad it will set P14 high. Once the pin is set, it will read the output of P10-P13 and stores it in the I/O register for use reference by the game.

External Link Port

The external link port is a 6 pin port mounted to the right of the DMG. The first amd last pins are power and ground, while the remaining 4 consist of 2 output, 1 input, and 1 unused. The are wired almost directly to the DMG, with only a resistor in the way. Pins 2 and 3 are the I/O pins, with pin 2 sending data and pin 3 receiving data. Pin 4 is not used. Pin 5 is the clock signal, and is able to both send and receive the signal, depending on if the Gameboy is the master of the connected systems.

More on the Board

One thing that caught my eye on the PCB was a set of 6 unused, soldered over holes that looked almost like test points. The are located at the top of the board, directly above the left side of the DMG processor. Of the holes, 3 are grounded and aren’t connected to anything else. The other 3 are connected to both the cpu and the screen ribbon connector port. On the CPU, it connects to Data1 (pin 50), Data0 (pin 51), and clock (pin 53), all of them output pins. I thought it might be like the external link port, but the Data1 and Data0 pins are outputs only; the external link port also has 6 pins, but it has dedicated input and output lines. I also suspected it may have been a rudimentary IR port, which was present on the Gameboy Color, but the Gameboy color uses 4 pins for the infrared communication, so I still don’t know the purpose of these points.

DC Converter Board

DC converter board front

DC converter board back

Board Labels: ALPS, VCC, G, DC, CONV, DMG

This power board attaches to the logic board via 4 wires, 1 read and 3 green. It takes the +6V input from either the battery or mains and converts it to +5V for all the logic and -19V for the screen.

This board fits sideways in a space between the battery compartment and the side of the case.

Audio Jack Board

Audio jack PCB front

Audio jack PCB back

This board is attached directly to the case with two screws. It is a very simple board, only containing 3 inductors, 2 capacitors, and the audio jack. It provides stereo sound (take that, Gameboy SP!).

It acts as a breakout board, all the heavy lifting is done on the logic board through the audio amp. The components on it are there to regulate the output and protect the logic board from damage, in case someone connects a headphone jack to some charge.

Conclusion

The original Gameboy DMG truly began Nintendo’s line of modern handheld gaming consoles. With it’s tiny screen and 4 colors it opened up a new world of games to millions of people around the world. It has become a lasting cultural icon and was the host of many games I lovingly look back on, like Pokemon Blue, Super Mario Land and Tetris.

Today the easiest way to revisit this console is through emulators or the “Virtual Console” system in later Nintendo consoles. Despite this, there is still something special to loading in some new AA batteries, popping in a game cart and tuning the contrast before setting in for some good old olive green gaming.

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A Look at the Gameboy DMG