Some info about Mega Drive expansion pinout

Started by Tak-MK, July 25, 2022, 10:47:48 AM

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Tak-MK

Hi there! \o/
I'm Tak-MK, or Tak, or Sergio; as you prefer.

The thing is that I can't edit this page on the wiki after login (https://gamesx.com/wiki/doku.php?id=schematics:megadriveexpport) so here's the info in case someone can edit it!
Also I sent this to the owner of the wiki by email but seemed that those accounts don't exist now :(

I was trying to check how actually does a Mega-CD powers on, and although motherboards aren't exactly the same, if you check the schematic (https://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:pc_bd_mega-cd_sub_bd_171-6115c-schematic-1_of_1.png), on the lower right, I "discovered" that NPN transistor TR3 needs 7V (in case of NTSC-J Mega Drive 1) from Mega Drive on its Base so the 9V from Collector goes to the Emitter, which is connected to ground.
This circuit is connected as Base on PNP transistor TR4 and, since it's now connected to ground, it allows the 9V from Emitter going through Collector, and then to Mega-CD motherboard.
That, and following this other schematic (http://gamesx.com/wiki/lib/exe/fetch.php?media=schematics:pc_bd_mega-cd_connect_bd-schematic-1_of_1.png), made me understood that pin A28/B28 of Mega Drive, goes through that bridge to pins A26/B26 in Mega-CD motherboard, which goes directly to pin 11 from power/audio board, which connects to Base to the NPN TR3 transistor.

I'm still learning these kind of things so sorry if my explanation was a complete mess :P Also English is not my main language.

In any case, this was to say to you that on the wiki/webpage (https://gamesx.com/wiki/doku.php?id=schematics:megadriveexpport and in https://gamesx.com/cartouts/gennyport.htm), A28/B28 pin explanation should be the opposite; they're not Vcc IN pins for the Mega-CD to power the Mega Drive, but the Mega Drive actually "switching on" that TR4 transistor from the Mega-CD, hence, powering it on (since it doesn't have a proper physical switch).

What I'm not sure, it's if that "/C_OE" Cartridge Output Enable relates to not powering on the Mega-CD if you insert a cartridge game (?). Just a supposition.

Thanks a lot for your site and have a nice day!

NFG

Now that you've posted on the forum you should be able to edit the wiki.

What email did you find for the 'wiki owner'?  🤔

Tak-MK

Quote from: NFG on July 25, 2022, 07:50:24 PMNow that you've posted on the forum you should be able to edit the wiki.

What email did you find for the 'wiki owner'?  🤔

Thanks! I'll edit later from PC then.
Emails were carts@gamesx.com and disclaimer@gamesx.com, found both on the old wiki (and I've sent an email too to the owner of the domain gamesx.com :P sorry for that just in case, although the email was protected and I only used a form).

NFG

Remarkable.  I didn't get any of these emails.  admin and carts were spam magnets.  I don't know what you found for the domain owner, the registrar I use doesn't reveal my details.  ^__^

I didn't think I was so hard to find.  =/

Tak-MK

Quote from: NFG on July 25, 2022, 08:09:23 PMRemarkable.  I didn't get any of these emails.  admin and carts were spam magnets.  I don't know what you found for the domain owner, the registrar I use doesn't reveal my details.  ^__^

I didn't think I was so hard to find.  =/

Ah no no, I got a reply from Google saying that those emails didn't exist so... :(
And the registrar email had a form so I suppose it sent an email but without me knowing the address :D
In any case I found this wiki/forum and figured it was a migration from the old place, so here I am hahaha

Thanks a lot again!