Search found 616 matches
- Thu Oct 11, 2018 7:18 am
- Forum: Megadrive/Genesis
- Topic: Bus Arbiter and IO Chip Access
- Replies: 28
- Views: 40551
Re: Bus Arbiter and IO Chip Access
EDCLK: This signal is 0/floating (wasnt a very clean 0) when /SRES, /M3 or /HSYNC are asserted(0). Otherwise it seems to be MCLK/4. (I tested with a 5k signal. Got a 1.25K out. I thought this this should /5, maybe it doesn't like the slow speed?) Does not seem to be affected by anything else. It sh...
- Wed Oct 10, 2018 6:42 pm
- Forum: Megadrive/Genesis
- Topic: Bus Arbiter and IO Chip Access
- Replies: 28
- Views: 40551
Re: Bus Arbiter and IO Chip Access
Did some probing on my model 1 va2. It has a 5308 arbiter, a 5309 IO chip and a 5345. For what it's worth, we have the schematics for the VA3 . Main difference from your VA2 is that the 5345 (EDCLK generator, probably just a PAL or GAL) has been integrated into the bus arbiter (5308) and given the ...
- Tue Oct 09, 2018 11:48 pm
- Forum: Megadrive/Genesis
- Topic: Cart Design Questions
- Replies: 70
- Views: 145192
Re: Cart Design Questions
When writing 8Bit numbers to even addresses, is pin B28 (lower byte write) taken low and pin B29 left high, and for odd addresses B28 is left high and B29 is taken low? Or visa versa? Or does it work differently? !LDSW (B28) goes low (which is the "active" level) for writes to odd addresses and !UD...
- Fri Oct 05, 2018 8:37 pm
- Forum: Megadrive/Genesis
- Topic: Aggregating Community Research
- Replies: 12
- Views: 14601
Re: Aggregating Community Research
Bumping this as I've added a number of additional links to the OP. I'm sure there's stuff I've missed, so feel free to suggest additions here.
- Mon Sep 24, 2018 8:18 pm
- Forum: Megadrive/Genesis
- Topic: 68k edge case: btst dN,#immed
- Replies: 12
- Views: 17092
Re: 68k edge case: btst dN,#immed
I then checked Galibert's microcode dump (see here , or here for all data he has) and confirmed the same thing. Oooh, I didn't realize he had gotten that far with decoding the microcode. I'll definitely have to check that out when I get time. The TL;DR version is: "btst dN,#immed8" shares microcode...
- Wed Sep 19, 2018 11:25 pm
- Forum: Sound
- Topic: Regarding the YM3438 on the Mega Drive...
- Replies: 11
- Views: 16924
Re: Regarding the YM3438 on the Mega Drive...
Which games? I haven't heard of widespread compatibility issues with the Teradrive (which as I previously mentioned has a discrete YM3438), but I'd happy to test some if you know specific games that have problems.l_oliveira wrote: ↑Wed Sep 19, 2018 9:11 pmIf it is not done that way, the YM3438 actually fails to work on a lot of games.
- Sun Sep 16, 2018 4:34 pm
- Forum: Sound
- Topic: Regarding the YM3438 on the Mega Drive...
- Replies: 11
- Views: 16924
- Thu Aug 09, 2018 8:16 pm
- Forum: Megadrive/Genesis
- Topic: Teradrive Hardware Info
- Replies: 3
- Views: 8391
Re: Teradrive Hardware Info
Wow, good job with this! Thanks! I always wanted to investigate this hardware more, but never found the time. Still quite a few unknowns if you suddenly find yourself with a bunch of free time :wink: Happy to share test code and/or IDA disassembly projects if that happens (though I know how hard fr...
- Thu May 31, 2018 5:17 pm
- Forum: Megadrive/Genesis
- Topic: Teradrive Hardware Info
- Replies: 3
- Views: 8391
Teradrive Hardware Info
First, let me start with a big thanks to Nemesis and piroxilin for providing Teradrive disk images and firmware images respectively. Having easy access to software/firmware to reverse was a big help. Now for the info I've figured out: M68K Memory Map (standard MD hardware omitted) 000000 - ??????: B...
- Fri Apr 27, 2018 6:16 pm
- Forum: Megadrive/Genesis
- Topic: Struct maros/syntax and naming conventions
- Replies: 6
- Views: 9189
Re: Struct maros/syntax and naming conventions
You should put a non-zero number after the rs.b/rs.w/rs.l as that's the number of elements of that size you're allocating. Not sure if that's causing your syntax error, but you definitely won't get the right results with zero.
- Thu Mar 01, 2018 7:46 pm
- Forum: Megadrive/Genesis
- Topic: Where do I start? I'm seeking technical documents.
- Replies: 40
- Views: 28531
Re: Where do I start? I'm seeking technical documents.
Check out this thread and the linked documentation.
- Mon Feb 26, 2018 6:45 pm
- Forum: Megadrive/Genesis
- Topic: Where do I start? I'm seeking technical documents.
- Replies: 40
- Views: 28531
Re: Where do I start? I'm seeking technical documents.
I wonder if the last line is correct - I mean, I can't display color 0 of any of the 4 palettes even if I use the tiles in a background? It is correct; however, the backdrop color (i.e. what's drawn in the borders or if all the layers above it are transparent) can be any of the 64 CRAM entries, inc...
- Wed Jan 10, 2018 8:03 am
- Forum: Controls
- Topic: IO Support Header Values
- Replies: 1
- Views: 8525
IO Support Header Values
I was wondering what values were legal for the IO support field in the standard Sega ROM header so I poked around a bit. This page from the official docs gives quite a few of them, but omits newer peripherals. Looking at the games in my collection I was able to fill in a few gaps and come up with th...
- Tue Nov 21, 2017 9:25 pm
- Forum: Megadrive/Genesis
- Topic: Sprite List Code Messed Up
- Replies: 28
- Views: 18110
Re: Sprite List Code Messed Up
Hm. I wonder if anyone ever transcribed the whole microcode portion of US4325121... having it as a searchable document would be a lot better, as well as less error prone because of how bad the scan is. I've got just shy of 100 transcribed which is pretty far from complete, though it probably covers...
Re: XE-1AP
Interesting. The comment does seem to be in line with what the code does (saves the 12 nibbles as 12 bytes in the buffer and pulls the A,B,A',B' state from the 11th byte rather than the 12th). Though it also suggests that A,B,C,D comes in the first nibble with E1,E2,Start,Select in the second. It lo...