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  • Joined: 22 Jul 2019
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GameGear LCD tinkering
Post Posted: Mon Jul 22, 2019 1:56 pm

first time poster, long time reader of the SMS Power forums.
I was talking with a friend over twitter about installing an LCD screen in a GameGear, and we're both aware of the McWill mod for doing this, but after some reading and digging (through all dead links) I kind of got curious to the work and effort that is involved in making this.

I was wondering if someone has information to share, or tell me what to start researching/looking up to make something similar?

The idea is to be able to do the following:

  • Purchase a TFT LCD
  • Connect the right signals from the GG board onto the screen
  • Perform any required scaling

I understand these are huge steps, and that I would need to convert the signals from the board and most likely upscale them to fit the display properly, but I've been searching the net for relevant information, and I can find complete kits/mods, but not the theory/schematics/information behind it for what is involved.

Just consider it a curiosity that I want to get sated.
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Post Posted: Mon Jul 22, 2019 2:54 pm
1. Be familiar with the types of protocol used to interface to LCD screens digitally in the early 90s and today
2. Reverse engineer the GG screen protocol
3. Make an FPGA design to convert from this to a new panel. Probably a framebuffer is needed.

It is difficult to find screens of the right size with the right resolution - I see some GBC mods with 320x288 panels which are ideal...
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Post Posted: Mon Jul 22, 2019 4:25 pm
Going to try and step through this in a more complex way but even this will be dumbed down a bit compared to what you need to know.
Like maxim said you'll need to become familiar with how the LCD screen interface works on both the GG and a modern sourced LCD.

You should pick an LCD that you can source back to if for whatever reason you break one or plan on producing more copies of your project.
Its very difficult to find screens the right size and resolution as the Game Gear, Exact resolution may not be necessary, if you can find one with double the resolution that would work as well. (also mentioned by maxim, some GBC screen mods do this).

Once you've picked a screen you need to study both how its interface and protocol work. This involves timing and signaling that can become very complex.
Not only do you have signal lines like
Red, Green, and Blue
H Sync, V Sync, and maybe C Sync
but timing protocols such as
the Horizontal blank, Horizontal front and back porch
as well as Vertical blank, and its front and back porch.
All of these need to be interpreted and translated from the GameGear to signals and timings appropriate to the new LCD that you have picked.

To translate complex groups of signal lines and their timing protocols and FPGA is necessary to process the information at a rate that will not compromise the overall output or timing of the image being displayed. By this i mean avoiding things like screen lag or artifacting.
You'll also need a buffer which is a tiny bit of ram used to hold the frame after its been translated.
An FPGA is a chip that can assume different hardware configurations when its programmed. For the purpose of this, itll be programmed to act as an ASIC for the new screen and drive that screen.
The FPGA will translate all timing and sync signals into ones that work with the new LCD that youve picked for your project, be mindful of the refresh rate and the front and back porches for the Vertical and Horizontal signals on both the GameGear and the new LCD since youll need to calculate a way to translate that over, this is even more so important if you use a screen that has a higher resolution than the original GameGear LCD. Then it will require screen doubling which can be done easily by adjusting the the pixel rate appropriately.
The FPGA will also most likely need to process the GameGear image over to one that matches values the screen can read, typically 24 bits per pixel is standard today where as the GameGear will only display either 12 bits per pixel or 6bits per pixel (in SMS mode). You'll need to come up with a function that can translate the 4 bits per color into 8 bits per color.

Extra info or things to start looking into, FPGA programming and LCD timing. theyre going to be your biggest hurdle to overcome. I recommend using Altera FPGAs since they and their JTAG programmers are relatively cheap. There are tons of prototype boards you can buy cheap online too to test your work out on. The next thing is finding a memory buffer as well.

I recommend watching this, he creates a video output circuit that is extremely similar to the SMS's and explains what each logic chip does. He also explains how to set up a memory buffer as well for and LCD to read off of. You wont need all of these IC's to make yours as they can be emulated within an FPGA.
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Post Posted: Tue Jul 23, 2019 7:11 am
I think unfortunately you’re coming at this from the wrong direction.

That I know of there are three people in the world who have made or are making a production GG screen replacement.

One was from Japan (I don’t know their name), McWill made one and BennVenn is also working on a screen which is supposed to be available soon.

The thing that these three people have in common is they’re we’re all well versed in electronic engineering first and gaming second.

I know McWill and BennVenn are both electronic engineers by trade.

Unless this is the space you are coming from I think you’re going to very quickly hit a brick wall.

You can get an idea of the signals you need from the board by reading the McWill install instructions. This give you the pin positions and identification that you need to get the digital video data off the GG.

Then you’re going to have to work out what to do with it
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Post Posted: Tue Jul 23, 2019 7:21 am
Thank you all for the input.
Seems I have my work cut out for me to tackle this problem, but the long explanations at least have given me a track to follow.

I've graduated as an Electronical Engineer, but I must admit I haven't done anything serious for a long time when it comes to electronics outside repairing faulty consoles, doing a mod like this is going to be a huge undertaking most likely.

As I said, it's a curiosity I want to sate, and at least I know what to look up now and where to start my path, so many thanks for that.
Should I receive some result somewhere, I'll be sure to post it back here.
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Post Posted: Tue Jul 23, 2019 3:03 pm
I think you can do it! Its honestly not the most difficult thing to do in the retro scene, specially if you have the tools. Its just a large amount of work, If you break it up into small chunks though like any other project, then it becomes easy. I hope you have an oscilloscope, you're going to need it.
The biggest struggle in my opinion is just sourcing an LCD.
Good luck!
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Post Posted: Mon Dec 23, 2019 4:28 pm
The person in Japan is Norix. His PCB was the first one released, and has some significant improvements over the McWill including much better colors and much lower power draw. However it doesn't have the different screen resolution modes :/

I had no idea about BennVenn, that is great, looking forward to that!
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