Search found 293 matches

by Charles MacDonald
Tue Jun 14, 2016 3:14 am
Forum: Megadrive/Genesis
Topic: A few questions :)
Replies: 15
Views: 14036

Re: A few questions :)

The Game Genie disables all the user-accessible registers when it is running a game. The only thing you could do is checksum the ROM and verify if it is bad or not, which would indicate the Genie was patching one or more locations. I can't remember if the Genie software fully clears out RAM and VRAM...
by Charles MacDonald
Tue Jun 14, 2016 3:10 am
Forum: Hardware
Topic: GBS-8220 fuzzy and green
Replies: 7
Views: 12259

Re: GBS-8220 fuzzy and green

I'd try gently pressing on around the edges of each of the surface mount chips to see if anything changes. That would indicate a bad solder joint where a pin isn't contacting the pad on the PCB well. Or press gently on the PCB to flex it a bit and see if there's any changes. I know the cables and Ge...
by Charles MacDonald
Sun Apr 24, 2016 10:34 pm
Forum: Megadrive/Genesis
Topic: Alright dudes, I need your help! (soft-reset bug)
Replies: 37
Views: 27631

Re: Alright dudes, I need your help! (soft-reset bug)

If the Z80 is held in the reset state (by $A12000) then busreq will never be asserted and the loop will never exit. This is because the Z80 reset logic has a higher priority than the bus request logic. Maybe check for any unintended writes to $A12000 in the sound/joypad routines and verify the Z80 i...
by Charles MacDonald
Sat Mar 12, 2016 8:59 pm
Forum: Demos
Topic: Virtua Worm for SEGA Genesis
Replies: 3
Views: 4984

Re: Virtua Worm for SEGA Genesis

Wow, very nice! Also impressed to hear music and some SFX too.
Given the limitations of the Genesis, the title screen came out well. :D
by Charles MacDonald
Sun Feb 14, 2016 1:05 am
Forum: Cartridge
Topic: SRAM write protect
Replies: 5
Views: 10594

Re: SRAM write protect

I opened a few carts today. I can confirm that at least Phantasy Star IV and Sonic 3 do not implement the write protect bit in either game. I wonder which other games would be candidates to look at? Off topic: My Super Street Fighter II cartridge had a modification compared to db-elec's, there's a 0...
by Charles MacDonald
Sat Feb 13, 2016 8:35 pm
Forum: Blabla
Topic: The calendar. Birthdays members of the forum.
Replies: 3
Views: 8506

Re: The calendar. Birthdays members of the forum.

Happy birthday! Thanks for all your contributions to this forum. :)
by Charles MacDonald
Fri Jan 15, 2016 6:30 pm
Forum: Cartridge
Topic: SRAM write protect
Replies: 5
Views: 10594

Re: SRAM write protect

It's in the 32X documentation that's floating around. Also I noticed Beyond Oasis (and perhaps others?) write to these Sega-defined mapper registers despite not actually having one (I checked a real cart), presumably as the development hardware had it. Since the functionality isn't present in the ca...
by Charles MacDonald
Fri Jan 08, 2016 12:19 am
Forum: Cartridge
Topic: Add feature to a cart
Replies: 12
Views: 22350

Re: Add feature to a cart

- how is it possible to generate DTACK ? I understood it means address is available on the address bus but who defined it (when it's ready) ? You assert DTACK when you detect the address range you want is being accessed, meaning /AS is low and the address lines match the address range you want. For...
by Charles MacDonald
Thu Dec 24, 2015 4:59 pm
Forum: Cartridge
Topic: Add feature to a cart
Replies: 12
Views: 22350

Re: Add feature to a cart

Sometimes you see communication methods where there is no handshaking (acknowledgement or status indicators) and I don't know how they are supposed to work reliably. :) I realized since the circuit has a 74HCT74 there's a 2nd flip-flop we can use, so I expanded the schematic a little. Now when you w...
by Charles MacDonald
Thu Dec 24, 2015 6:33 am
Forum: Cartridge
Topic: Add feature to a cart
Replies: 12
Views: 22350

Re: Add feature to a cart

So, if I want to add an AVR on a cart and to control, from it, several others modules (ex: bluetooth for faster serial transfert) how could I power it ? It's OK to just use the +5V from the cartridge port directly, it seems unlikely what you are adding will use more current than is available. Other...
by Charles MacDonald
Wed Dec 02, 2015 2:10 am
Forum: Hardware
Topic: Decapping more Genesis chips
Replies: 17
Views: 62287

Re: Decapping more Genesis chips

about SCSP DSP docs - there (almost) none of it. if I not mistaken, most of info comes from Dreamcast AICA docs, there is some brief explanation what its opcode bits means and how its workflow is. but it lacks of details. That's too bad. What would approach would you suggest for figuring out how th...
by Charles MacDonald
Tue Dec 01, 2015 9:31 am
Forum: Hardware
Topic: Decapping more Genesis chips
Replies: 17
Views: 62287

Re: Decapping more Genesis chips

Decapping can be useful when the chip has ROM inside it. The SMPC and SH-1 from the Saturn would be good candidates for this as we don't have dumps of the internal ROM from either one. I think somebody tried and failed to do it with the SH-1 in the past, likely due to the complexity. But the SMPC wo...
by Charles MacDonald
Sat Nov 14, 2015 8:52 pm
Forum: Hardware
Topic: Game Toshokan
Replies: 10
Views: 12421

Re: Decapping more Genesis chips

Mine seems to be Rev. A too (the mask ROM is marked "MPR-12750A-T") When I run it (I don't have a modem) it displays a message in Japanese with the word "OFF". Any idea if that relates to the modem or is a region check warning? Has anyone tried faking the modem responses to see what it tries to do o...
by Charles MacDonald
Fri Nov 13, 2015 7:01 pm
Forum: Hardware
Topic: Game Toshokan
Replies: 10
Views: 12421

Re: Decapping more Genesis chips

Well now I'm confused. All that's inside the Game Toshokan cartridge is a ROM, some TTL logic, and a small X24C01 serial EEPROM. I see the retail box includes a modem and a cartridge and nothing else. So where do the downloaded games go? :? I made a schematic of the board to figure out the memory ma...
by Charles MacDonald
Sat Oct 31, 2015 10:19 pm
Forum: Hardware
Topic: Game Toshokan
Replies: 10
Views: 12421

Re: Decapping more Genesis chips

Yeah 128K of RAM does sound like quite a lot. I ordered one and I'll report back once it arrives and I have it opened up. If it's just two 64K RAM chips I'll be really surprised -- I wonder what the retail price of Game Toshokan was back then. Had to be expensive.