Genesis/Megardrive Master System Compatibility Mode

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phoboz
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Genesis/Megardrive Master System Compatibility Mode

Postby phoboz » Fri Jan 05, 2018 1:18 pm

Does anyone know how to put the Genesis/Megradrive in Master System Compatibility mode?

The power base converter made that possible for the original hardware by connecting some pins to GND, or VCC.
However, I guess the core itself has to do something to react on this configuration also, e.g. to load the rom code into the Z80 address space etc.
Do I need to change the addressing somehow, disable the m68k etc.
Please reply to this if you have more information on how the Genesis/Megadrive was set up in order to play Master System games?

Also if anyone knows if there is a Genesis/Megadrive game that uses the Master System video mode, please tell me?
If I would have such game, I could at least start by testing the Master System video of of the FPGAGEN VDP and see if it's working correctly.
If no such game exists, maybe a possibility would be to program a small demo Genesis rom using the Master System Video mode?
I know that there are some tools on the net for programming new Genesis/Megadrive games.

The reason for asking these questions is that I want to enable the possibility to play Master System Games in the FPGAGEN core.
It would be easier to maintain one core FPGAGEN instead of having a different core for Master System. Which no one seems to attend to anymore...

:cheers: Happy New Year 2018

hyperterminal
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Re: Genesis/Megardrive Master System Compatibility Mode

Postby hyperterminal » Fri Jan 05, 2018 1:35 pm

You better ask these question at http://www.smspower.org. This is where all the Master System experts are.

Here you can read on how to force the Genesis into SMS mode: https://db-electronics.ca/console-tech/ ... /sms-mode/

The Genesis' VDP only supports the Master System VDP's mode 4 (though it cannot run in modes 0, 1, 2, or 3). Therefore SMS games such as F-16 Fighting Falcon are incompatible with the Genesis and will only give you a black screen.

Sorgelig
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Re: Genesis/Megardrive Master System Compatibility Mode

Postby Sorgelig » Fri Jan 05, 2018 5:21 pm

Genesis core has no Master System mode. You are welcome to improve the core :)
There is separate SMS core, but game compatibility is so-so.

phoboz
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Re: Genesis/Megardrive Master System Compatibility Mode

Postby phoboz » Fri Jan 05, 2018 6:04 pm

Sorgelig wrote: There is separate SMS core, but game compatibility is so-so.

Yes I have played around a bit with the SMS core, and it's not perfect.
That's the reason I want to be able to play sms roms using the Genesis core instead.
Obviously not all games will work, but my experience using a powerbase mini with the retrobit - super retro trio, most master system games I like works (which does not work with the SMS core)

The video counting is not implemented correctly in the SMS core, e.g. the screen is cropped horizontally. Rather a special way of counting is implemented in the sms mode of the FPGAGEN vdp. Which I assume should make the pixels a little bit wider, thus the 256 pixels are covering the whole screen instead of the need to have 320 narrower pixels to cover the whole screen.

I figured out that one of the trix must be to hold the m68k is reset all the time.
https://db-electronics.ca/console-tech/sega-genesis-megadrive/sms-mode/ wrote:With the above connections, the cartridge port loses the #RESET signal on B27 – it now constantly outputs GND instead of a nice active-low reset pulse


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