Search found 2387 matches

by TmEE co.(TM)
Thu Jan 16, 2020 12:34 pm
Forum: Hardware
Topic: Cartridge slot questions
Replies: 22
Views: 1072

Re: Cartridge slot questions

MD2 VA0 and VA1 do not have 75ohm load on the cartslot signals. 32X just has very low output impedance amp that can drive headphones (i.e 16 ohm load), there's no variation in output level due to it. You just need a beefy amp to make things work.
by TmEE co.(TM)
Thu Jan 16, 2020 10:29 am
Forum: Hardware
Topic: Cartridge slot questions
Replies: 22
Views: 1072

Re: Cartridge slot questions

Sik wrote:
Thu Jan 16, 2020 12:44 am
Anyway, if I'm understanding correctly this means the audio output (as far as the cartridge slot goes) is ±2V, excluding bias?
Yup, +/-2V into 75ohm load is the target for cartslot audio.
by TmEE co.(TM)
Thu Jan 16, 2020 12:25 am
Forum: Hardware
Topic: Cartridge slot questions
Replies: 22
Views: 1072

Re: Cartridge slot questions

The clipping is due to the mixing+amp chip, it isn't rail-to-rail IO capable (but it can get very close to ground due to special design, with top side being typical ~1V shy from a power rail) and due to it there will be early clipping. If the attenuated and filtered PWM signal was given a DC offset ...
by TmEE co.(TM)
Wed Jan 15, 2020 5:43 pm
Forum: Hardware
Topic: Cartridge slot questions
Replies: 22
Views: 1072

Re: Cartridge slot questions

I have not seen the edit, I was waiting for a new post lol. I'll do measurements soon. 32X audio output is almost 4Vpp on the cartslot pins, and it clips early, both tips of the sine are flat. There's a 45Hz -3db point high pass filter forming in most MDs (47µF cap in 32X, 75ohm load on most MDs). A...
by TmEE co.(TM)
Fri Jan 10, 2020 4:19 am
Forum: Cartridge
Topic: Designing MD sdcard flashcart for fun, advice?
Replies: 13
Views: 3608

Re: Designing MD sdcard flashcart for fun, advice?

That is a pretty nice writeup ~
by TmEE co.(TM)
Thu Jan 09, 2020 9:37 am
Forum: Hardware
Topic: Cartridge slot questions
Replies: 22
Views: 1072

Re: Cartridge slot questions

Someone make me a 32X test ROM with same sort of grayscale ramp as seen here : viewtopic.php?f=22&t=2188

And while at it, play a full scale sinewave on both L and R side, I'll get the scope out and measure the levels at various points.
by TmEE co.(TM)
Mon Dec 09, 2019 10:29 pm
Forum: Megadrive/Genesis
Topic: M68K Bus Control and Vdp
Replies: 25
Views: 1868

Re: M68K Bus Control and Vdp

68K duplicates high and lwo bytes during 8bit writes (i.e $12 is $1212 on the bus). Reads are aways 16bit and CPU internally chooses which half to use depending on address.
by TmEE co.(TM)
Tue Nov 26, 2019 1:31 am
Forum: Tools
Topic: Aseprite Mega Drive Digitizer
Replies: 10
Views: 2314

Re: Aseprite Mega Drive Digitizer

Computer composhit output would look nothing like the MD output (i.e near complete lack of various artifacts) and you still have the problem of non-linear level ramp that most emulators and tools don't treat right from what I know ( http://gendev.spritesmind.net/forum/viewtopic.php?f=22&t=2188 ). Th...
by TmEE co.(TM)
Mon Nov 18, 2019 9:42 pm
Forum: Megadrive/Genesis
Topic: Noob questions: DEFINITIVE info about Z80 BUSREQ, RESET?
Replies: 28
Views: 6875

Re: Noob questions: DEFINITIVE info about Z80 BUSREQ, RESET?

I haven't had any issues by doing a shorter than 192 cycle reset, but I always explicitly zero out all the YM registers and it seems internal state is also fine.
by TmEE co.(TM)
Fri Nov 15, 2019 12:53 pm
Forum: Megadrive/Genesis
Topic: DMA and FIFO
Replies: 11
Views: 2923

Re: DMA and FIFO

68K User manual suggests it is based on bus cycles rather than instruction cycles, I got the impression you can get the bus while an instruction is still halfway done. The processor asserts BG as soon as possible. Normally, this process immediately follows internal synchronization, except when the p...
by TmEE co.(TM)
Thu Nov 14, 2019 12:48 am
Forum: Video Display Processor
Topic: Upload speed on display time
Replies: 2
Views: 943

Re: Upload speed on display time

There's 16 or 18 access slots spread around one line during rendering, depending on 256 or 320 pixel mode, each capable of accepting one byte so 16 or 18 bytes are possible to transfer in best case during a line. 4x 68K cycles is 3.5 pixels, these access slots come in triplets that are 16 pixels apa...
by TmEE co.(TM)
Sun Oct 27, 2019 3:33 pm
Forum: Cartridge
Topic: Designing MD sdcard flashcart for fun, advice?
Replies: 13
Views: 3608

Re: Designing MD sdcard flashcart for fun, advice?

If it is a proper NOR flash it'll take more than 100k writes before the flash fails. Overall the idea looks doable but I'm not sure if you can cleanly supply NOPs to the 68K and later get it execute something more useful. If I were you I'd pull !MRES low (this signal you can drive yourself, but only...
by TmEE co.(TM)
Thu Oct 03, 2019 7:18 pm
Forum: Controls
Topic: New device letters
Replies: 20
Views: 4983

Re: New device letters

Ok, so you support the Saturn stuff in your game ? How would the MD port pins be connected to the Saturn port ? I'm not sure any standard exists...
by TmEE co.(TM)
Sun Sep 29, 2019 11:42 am
Forum: Controls
Topic: New device letters
Replies: 20
Views: 4983

Re: New device letters

Use lowercase letters too not just uppercase ones, or perhaps just set the top bit to show it is saturn peripheral and not MD.