Master System on Mega Drive ( via Phantasy Star 1 pcb)

[barneygumble]

I think it was mentioned and discussed before.
Phantasy Star 1 was re-released for the Mega Drive in Japan ( G-4534) in 1994 - ( kind of with the PH4 release )
and its Rom on the PCB is actually simply the Sega Master System Rom.

I opened up my cart of PH1 and it indeed holds a different PCB that I usually seen at MD Games.
The Mask Rom :

MPR-16266-F
834011
2A5 AK
9402 T00
( ROM 32pin)

The PCB : 171-6590B

Would it be possible to swap the Maskrom with an eeprom (which one would fit ? )
Of course the simplest way would be buying a Master System adaptor, but still it would
offer a possibility of a English Translated Phantasy Star 1 on a MD Cart.

[Sik]

I don't see any reason why you can't, as long as the pinout is the same (unless you replace the whole PCB). Setting the console into Master System mode is literally just a matter of wiring a line in the cartridge slot (some other lines get repurposed, but as long as you stick to what that cartridge does you should be safe).

[tokumaru]

How does this game handle the pause button?

[Sik]

This game doesn't need pausing ^^; (nothing is dependent on timing so you can just press nothing and the game will just idle)

[tokumaru]

How convenient. Well, this might be an issue if you replace the game for one that does require pausing then. IIRC, the pause button on the SMS generates an NMI, right? Is that as simple as closing a swich or do you need more complex hardware?

[Sik]

Just a switch which is connected to one of the cartslot pins (that tells the console to generate NMI). That's how the pause button in the Power Base Converter works.

[tepples]

Can SMS games read the Start button of a connected Genesis controller? If so, a pause patch would work.

[Sik]

Yes, you can even make them read all the buttons from a 6-pad if you really want to.

Note that this would require expanding a joypad reading routine (it will inevitably happen due to having to read twice for a 3-pad, seven times for a 6-pad) so it would probably require moving code around. And this is before you patch the game to implement pausing through the Start button.

Just make sure to not do what the Master System port of Sonic Blast does (they moved pausing to the 1 button... WTF? - makes sense in context because on the Game Gear the Start button is a proper polled button and not NMI, but still)

[tokumaru]

Yes, you can even make them read all the buttons from a 6-pad if you really want to.

Do you even need a Genesis/MD for that or can an actual Master System with a Genesis controller do it too?

Just make sure to not do what the Master System port of Sonic Blast does (they moved pausing to the 1 button... WTF? - makes sense in context because on the Game Gear the Start button is a proper polled button and not NMI, but still)

Since Sonic uses a single action button, I don't think this is such a big problem. I can imagine people who are used to jumping using the button that now pauses being pissed off, but the convenience of being able to pause without getting up is more than welcome IMO. I'm not talking out of laziness, it's more the fact that the time it takes for you to get up and press the button could end up costing you.

[ccovell]

Would it be possible to swap the Maskrom with an eeprom (which one would fit ? )

Many (most) SMS games have a ROM with a built-in memory mapper, so you can't just use an (E)EPROM... unless you want yourself limited to 32k homebrew and such. The forums and info pages at smspower.org have more information.

[tepples]

I wonder why Nintendo never did that in the NES and Super NES era. I imagine it would have saved pins to put the mapper in the PRG ROM.

If you're making your own Master System game, you could put in your own mapper circuit, such as a 74HC161+74HC08 or an MBC5 clone or something like that, correct?

[lidnariq]

I think the only reason to not(?) do that is that there's almost no funny mappers for the SMS, just the "32KiB mapped from 0x0000-0x7FFF" and "three 16 KiB banks mapped in the bottom-most 3/4 of the address space": http://www.smspower.org/Development/Mappers

It would be easy to recapitulate something like NROM-368 using just a single AND gate, though.

[Sik]

Yes, you can even make them read all the buttons from a 6-pad if you really want to.

Do you even need a Genesis/MD for that or can an actual Master System with a Genesis controller do it too?

Master System can do it too.

Just beware, this works with joypads but not with other accessories which need reconfiguring the I/O lines differently. The Master System has limits on how much you can repurpose them, unlike the Mega Drive where every bit can be input or output.