Search found 284 matches
- Wed Jun 06, 2018 12:05 pm
- Forum: Video Display Processor
- Topic: disable video on vblank, better?
- Replies: 7
- Views: 5376
Re: disable video on vblank, better?
Unfortunately it doesn't speed anything up, the access time during V-Blank is the same as when the screen is turned off. However you can get more time to do DMA transfers by "letterboxing" the display, where you turn off V-Blank early (say line 200) and then back on late (say line 8 of the next fram...
- Mon Jul 31, 2017 2:06 am
- Forum: Blabla
- Topic: Alien Soldier graphic glitch
- Replies: 2
- Views: 4036
Alien Soldier graphic glitch
I've seen an issue on some flashcarts and my own dev hardware where there are graphical glitches in this game, during the 7 Force battle when you fight the cat robot thing. It's happened with several different Genesis consoles. Here's how it should look: https://youtu.be/AaSsBtFD4Xc?t=182 Now what I...
- Mon Jan 02, 2017 2:42 am
- Forum: Video Display Processor
- Topic: Mode 4 VRAM Timing
- Replies: 4
- Views: 5018
Re: Mode 4 VRAM Timing
Wow, great job! Nice to have a very technical post to start the new year. :) About the sprite Y read parts, any idea why it goes up to 15 and not 7 given that there's eight possible sprites per scanline? Or is this a side effect of having to read data in some wider width? (say 16 bits at at time, so...
- Thu Aug 18, 2016 8:27 pm
- Forum: Megadrive/Genesis
- Topic: Questions on developing a Mega Drive emulator
- Replies: 39
- Views: 12066
Re: Questions on developing a Mega Drive emulator
Mask of Destiny, good catch! I've edited my post for clarity. unlicensed EA games (Budokan, etc.) use H40 mode with the wrong combination of RS1,RS0 set, How does that even work, that should result in an invalid TV signal. For one of the combinations of bits yep, it's a scrambled mess, for the other...
- Thu Aug 18, 2016 4:21 pm
- Forum: Megadrive/Genesis
- Topic: Questions on developing a Mega Drive emulator
- Replies: 39
- Views: 12066
Re: Questions on developing a Mega Drive emulator
Bart did a good write-up on some poorly documented/undocumented aspects of the 68000 too: https://emu-docs.org/CPU%2068k/68knotes.txt Other quirks include: MOVEM reading one address past the source location: http://gendev.spritesmind.net/forum/viewtopic.php?f=13&t=2010&p=25882 CLR to memory being re...
- Mon Jun 27, 2016 3:08 am
- Forum: Megadrive/Genesis
- Topic: Z80 and DMA
- Replies: 1
- Views: 1954
Z80 and DMA
When doing DMA from the 68K address space to VRAM, what happens when the Z80 tries to read banked RAM memory during a long transfer? I'd assume the Z80 is halted until DMA is over, but I think this would affect sample playback. Is there a priority system where the Z80 can always complete an access f...
- Tue Jun 14, 2016 3:14 am
- Forum: Megadrive/Genesis
- Topic: A few questions :)
- Replies: 15
- Views: 7538
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...
- Tue Jun 14, 2016 3:10 am
- Forum: Hardware
- Topic: GBS-8220 fuzzy and green
- Replies: 7
- Views: 6377
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...
- Sun Apr 24, 2016 10:34 pm
- Forum: Megadrive/Genesis
- Topic: Alright dudes, I need your help! (soft-reset bug)
- Replies: 37
- Views: 11886
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...
- Sat Mar 12, 2016 8:59 pm
- Forum: Demos
- Topic: Virtua Worm for SEGA Genesis
- Replies: 3
- Views: 2745
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.
Given the limitations of the Genesis, the title screen came out well.

- Sun Feb 14, 2016 1:05 am
- Forum: Cartridge
- Topic: SRAM write protect
- Replies: 5
- Views: 5817
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...
- Sat Feb 13, 2016 8:35 pm
- Forum: Blabla
- Topic: The calendar. Birthdays members of the forum.
- Replies: 3
- Views: 4753
Re: The calendar. Birthdays members of the forum.
Happy birthday! Thanks for all your contributions to this forum. 

- Fri Jan 15, 2016 6:30 pm
- Forum: Cartridge
- Topic: SRAM write protect
- Replies: 5
- Views: 5817
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...
- Fri Jan 08, 2016 12:19 am
- Forum: Cartridge
- Topic: Add feature to a cart
- Replies: 12
- Views: 11355
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...
- Thu Dec 24, 2015 4:59 pm
- Forum: Cartridge
- Topic: Add feature to a cart
- Replies: 12
- Views: 11355
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...