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[Novaline]

You might find this interesting.

I bet you would love one of these!

http://hem.bredband.net/hensam/ggtv.rar

[Maxim]

[Novaline]

[Bock]

In the directory Maxim mentionned, there's three (bad quality) pictures of the same Game Gear with the same board as your Game Gear.

I took those pictures a while ago. The schematic stuff are because people started working on replicating the mod, but you're right that noone got it to work perfectly as of yet.

Notice your Game Gear is serial number B4U000038 and mine B4U000105.
They are from the same batch given to developers. May I ask, where did you obtain it?

Thanks for your picture btw. Mine are outdated and not of good quality. With your permission, I'll add your pictures in the same directory.

[Novaline]

[Bock]

Does he have reference of the auction url/number? Just for curiosity, to see the description. And, I may try to ask the seller from where does it come from.

$75 is a good price. I was supposed to pay $50 for mine but kinda got ripped off by the seller who got away with a $150 check (for a complex reason) and stopped answering to me. Anyway even at this price I would have bought it.

It's not necessary to remove old pictures, all pictures may be informative so I'll keep the old pictures and add the new ones if they come.

May I get in contact with the guy? I do also collect GG, maybe we could exchange a few things.

Do you have problems quoting texts? (I wonder if this forum is easy to use for everyone). The starting quote BBcode was missing here so the quoted part of your message doesn't look like a quote. You can edit and fix your message if you understand the problem, else I'll do it for you.

[DJ]

If you look at photo 100_1489.jpg (ggtv.rar) from Novaline you will notice that there is anothe IC under the 315-5242 chip. Does anybody know what this chip is or have other photos of the GGTV board from the side.

I presume that there are at least 6 IC's on the GGTV board as you can see
the following:

IC1 - SEGA 315-5242
IC5 - 74HC175A
IC6 - 74HC00A

The board does not look terribly hard to make if we could obtain a few more details on the other chips and connections. IC1 can be obtained from SEGA system 18,24 arcade boards and IC5,IC6 are standard 7400 chips.

I have had some limited success with getting the GG on TV but I have not got right colours yet.

Does anyone have anymore info?

[Charles MacDonald]

[xavier]

Actually I tried an RGB decoder on my european Gamegear (with classic component don't be affraid ).
I think there is only 4bits for color, see my little calcul:

4bits=16 values SO 16red x 16 green x 16blue =4096= Complete GG palette

I built a working module with 3 4bits latch ( data pins c66 c59 c60 c61) each connected to an R2R DAC
, I take T2 pin as Sync signal.

The 3 latchs are driven by a 2->4 decoder connected on C75 and FB1

It give a stable image with red and blue correcly displayed but the green is corrupt.

I think the latch are not correclty driven. I tried replace decoder by binary counter ( C75 as clock) but it dont work.

Anyway I think the first part: Latch+DAC is correct.

Any Idea?

NB: on my GG the motherboard is different than all picture I see on internet. Maybe an old version?

[DJ]

Thanks Charles and Xavier.

No doubt you have seen Chris Covell's and Victor Kemps site on the GGTV. The photos on these sites (if there are correct) show the data connections as being 4 bit.

Some of the inputs of the 7400 are tied together and the outputs chained to other NAND gate, so maybe this is just buffering some of the signals.

Another thought I had for the 74175 is that they might be used for dividing the clock signal to make the pixel clock. The crystal on the GG runs at 32.2159Mhz so I guess the pixel clock (5.36Mhz) must be the main clock divided by 6?

Xavier, there are at least two versions of the gamegear (old and new) that I am aware of. I bought a copy of the GG (both old and new versions) schematics a while ago and have been using these in my attempts at the GGTV.

Working from the GGTV photos and circuit diagram I tried to match the up the GG connections to GGTV. These are only guesses but this is what I have so far.

Old Version GG (1 ASIC)

Pin 1 - C22/R13 (Data)
Pin 2 - C23/R14 (Data)
Pin 3 - C24/R15 (Data)
Pin 4 - C25/R16 (Data)
Pin 5 - T2 (Composite Sync)
Pin 6 - T7
Pin 7 - T1 (CPU Clock) 3.58Mhz
Pin 8 - T13
Pin 9 - T10 or T11?
Pin 10 - T10 or T11?
Pin 11 - C11+ +5v
Pin 12 - C11- Gnd
Pin 13 - T12 Audio Gnd
Pin 14 - T8 Left Speaker
Pin 15 - T9 Right Speaker

T10 - T11

I don't own an old version GG so I then tried to match up the above connections to a new version GG.

New version GG (2 ASICs)

Pin 1 - C59/R54 (Data)
Pin 2 - C60/R55 (Data)
Pin 3 - C61/R56 (Data)
Pin 4 - C62/R57 (Data)
Pin 5 - T2 (Composite Sync)
Pin 6 - T7
Pin 7 - T1 (CPU Clock) 3.58Mhz
Pin 8 - ?
Pin 9 - T10 or T11?
Pin 10 - T10 or T11?
Pin 11 - C6+ +5v
Pin 12 - C6- Gnd
Pin 13 - T12 Audio Gnd
Pin 14 - T8 Left Speaker
Pin 15 - T9 Right Speaker

I can't find T13 marked on the new version of GG. It does not seems to appear on the board or circuit. I don't know how important this signal is and if it is possible to use a GGTV with the newer versions of GG.

You sound like you are on the right track with your latches + DAC. I would be interested in looking at the circuit you have so far.

[Charles MacDonald]

[xavier]

DJ and Charles, thanks for the info,
Indeed Chris Covell's and Victor Kemps site was of great help :)
Here my output part schematic:



latches are 3 x 74HC574 (unused part is for upper 4bits) or 2 x 74HC075 (less easy to find but take less space), plus if you can found the new 74Fxxx it's better.
The DAC are typical R2R ladder, 2R can be from 390 to 470 ohm depending of your TV quality. Sadly R must be created by putting in parralel 2 2R resistors wich increase space.
Maybe a simple Binary Weighted DAC wich require only 4 resistors can be used, but correct resistor value are rare if not impossible to found ( You can however try with rounded values)!
For simplicity sake, test can be made by using an unique resistor of 330 ohm connected on the MSB of each latches ( with this configuration gradient 'll not be displayed but it's enough to test colours separation)

For the command part...
well it's not so simple, if you take signal from the missing C75 (new PCB version) inject it in "RED valid" and invert it into "BLUE valid" you obtain red/blue separation but green seems to be mixed in the 2 other colours:



So a decade counter could do the trick ( first pulse red, second green and third blue) but my test with a standard 4017 give nothing, but according to DJ, 74175 + counter should be the answer. I'm sure It's just a timing problem!

Another interresting signal is FB1 ( Fast Blanking ?).

NB: And now a really bad joke, during my first test I used a 2->4 decoder driven by C75 and FB1 to control the 3 latches and I forget to connect OE of RED latch to ground, strangely the screen appeared nearly CORRECT???
I had just time to take a screnshoot:



Since then I never obtain so good image. Call that Murphy law...

[edit by Maxim: replaced huge image with clickable thumbnail]

[Charles MacDonald]

[xavier]

[xavier]

IT WORKKKKKKK!!!!!!
But don't ask me how.?!?!

I just replace R2R DAC by Charles version, connect RED valid to C75, BLUE valid on FB1 and GREEN valid on a pin of IC2, and it work!

Red seems a little too strong but maybe the DAC value are not perfect ( I use rounded value plus I need to filter the output signal)
So blue tend to appear purple.

Here with Sonic GG:


And with Castle Of Illusion ( GG version but work in SMS mode):


T10 and T11 must be tied, if not SMS mode looks horrible.

My only guess is FB1 is set when blue data is yet avaible on data bus, allowing easy access to it, however we can't use it to blank latches after that, but it don't seem a big problem...

I'll post a valid schematic as soon as possible.

[DJ]

Congratulations Xavier,

The GG photos look great. It looks like you have solved it.
Funny how a simple R2R + Latches can do the same job as a complex GGTV.

On my schematics FB1 is shown as an optional ferrite bead. FB1 connects through a 1K resistor to the X1 Crystal (32.215Mhz). C75 is shown as a junction between pin 10 U2 & pin 6 U3.

Charles,

Here is the link to where I brought the GG schematics from. (You wouldn't believe how many google searches I did to find them!). They are not the official SEGA schematics but have been reversed engineered. They are still fairly detailed.

[/url] http://w3.trib.com/~rollo/

Back to the discussion on the GGTV pixel clock, if the pixel clock is running at 5.36Mhz what must be the speed of the R,G,B coming from the 4-bit bus? 3 x 5.36Mhz? 4-bits of R,G,B would need to be present (latched) on the 315-5242 inputs ready to be clocked by each pixel clock.

Also, how did you calculate the pixel clock.

I took 15.734Khz / (256 pixels across + 64 (video blanking,etc)) and got 5.035Mhz. I then rounded this up the the nearest multiple of the main clock, which would give 5.36Mhz. Is this correct?

A 5.36Mhz pixel clock probably means there is about 340 pixels in total across the GG screen.

[Jan Solrac]

weeeeeeeeeeeeeeeeeeeeeeeeeeee...
impressive !

post your results guys!!!
god bless u...

lol

[xavier]

I don't forget you ;)
I'll post the revised schematic this week-end.
Thanks to DJ info, I improved the display quality and now colors are perfect.
Since I did a mistake and take FB1 as Fast Blanking (wich give incorrect blue), I must use another signal as Blue valid, such signal don't seem to exist on GG board so I use a little trick, I take a signal very near and use RC filter to tweak it ( I know it's terrible) there is however a little problem, sometime glitch appear with certain colour combinaison, it's rare and very small but... its not perfect.
Keep in mind it's a hack, I don't think the original GGTV use the same principle.

[Charles MacDonald]

[asynchronous]

I think only 1 of the D-latches in the 74HC175 is required to divide the main 32MHz clock by 2 to create 3 clock cycles per pixel (32MHz / 2 = 15MHz = 3 x 5MHz - the pixel clock).

One of the NAND gates could then be used to create the missing "Valid_Blue" signal from the present "Valid_Red" and "Valid_Green" signals.

Then use the remaining 3 NAND gates to combine the 15MHz clock signal with the 3 "Valid" signals to create the 3 latching signals for each of the RGB colours.

All this depends on the exact operation of the "Red_Valid" and "Green_Valid" signals from the gamegear, but it's how I see it working.

Oh, and never, ever, use 4000 series logic in MHz-speed systems. You're asking for trouble.

I hope this helps with the final solution.