Search found 2308 matches

by TmEE co.(TM)
Thu Sep 20, 2018 4:37 am
Forum: Sound
Topic: Regarding the YM3438 on the Mega Drive...
Replies: 11
Views: 286

Re: Regarding the YM3438 on the Mega Drive...

Hellfire reads status from the wrong ports and has music slowed down by half, same happens on a stock MD2 also. With proper analog parts, 3438 is much cleaner and waaaaay less noisy than 2612. The output pulses are much wider and amplitude greater, SNR is greatly increased.
by TmEE co.(TM)
Sun Sep 16, 2018 6:03 am
Forum: Sound
Topic: Regarding the YM3438 on the Mega Drive...
Replies: 11
Views: 286

Re: Regarding the YM3438 on the Mega Drive...

I have not got any sort of issues on YM3438 with doing continuous reads on MD and over LPT port. Neither have clock that is equal or higher than the YM though.
by TmEE co.(TM)
Tue Sep 04, 2018 9:59 am
Forum: Exodus
Topic: Exodus 2.1 release soon (Now available!)
Replies: 28
Views: 1116

Re: Exodus 2.1 release soon (Now available!)

I haven't found any sort of timing difference between VRAM activity and whatnot between MD and SMS mode, all the access patterns are identical, video timings identical (AND different from H256 timings). What is different is the FIFO interface being active and no support for updating only the lower h...
by TmEE co.(TM)
Fri Aug 24, 2018 2:21 am
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

LM4880 seems to be adequate. It has better THD and PSRR and looks to be just as easy to use. It should be noted that the output is inverted compared to input (but this has no consequences usually). Only opamps made to drive 75ohms are video stuff but they're usually unsuitable for audio for the most...
by TmEE co.(TM)
Wed Aug 22, 2018 4:03 am
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

All opamps can have the negative power go to GND, and as with all opamps you then have to bias the inputs to somewhere between GND and positive power rail in such case. Now as far as NJM2073 goes, it isn't a regular opamp but a special purpose thing which has internal biasing to reduce external part...
by TmEE co.(TM)
Sat Aug 18, 2018 3:33 pm
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

MD biases the signals to its own needed offsets, there's series capacitors on all the signals which are there for that purpose. It is all AC coupled. You cannot do full 5V swing for similar reasons as you get in the cart, the machine still only has 5V power rails. You'll have to experimentally find ...
by TmEE co.(TM)
Sat Aug 18, 2018 2:01 pm
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

First of all signal from the DAC etc. is not gonna have a negative components so it is already biased above 0V. You will have to bias it exactly to 2.5V for best dynamic range with most opamps and also bias the opamp to that voltage also. You can use a small linear reg for that or some resistors+cap...
by TmEE co.(TM)
Tue Jul 31, 2018 12:49 pm
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

You'll be up for plenty of manual work. I have worked with pulls in past and you absolutely have to verify them all, out of 700 chips, around 100 were dead or damaged (i.e parts of it not programmable etc.). Also pins way not be in the best shape, causing difficulties when soldering. Those stocks ca...
by TmEE co.(TM)
Fri Jul 27, 2018 2:03 am
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

EPROMs have not been produced for years, if you're lucky you can get new-old-stock but you're very likely to get pulls. Your only option is 3.3V parts, having the level shifters and then exclusively using 3.3V parts will cost less than trying to get 5V stuff together. There's far more options and mo...
by TmEE co.(TM)
Tue Jul 24, 2018 4:24 pm
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

That EPROM will work but availability might be limited if you intend to make lot of cartridges. They are also likely to be pulls rather than new parts. To save a looooot of time make sure the parts you order are erased before hand. It takes half an hour at least to erase an EPROM. If the MCU has 5V ...
by TmEE co.(TM)
Tue Jul 17, 2018 8:42 am
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 21
Views: 1214

Re: Cart Design Questions

You need full level conversion, resistors aren't going to do anything but current limiting. For single direction stuff you could get away with voltage dividers but signal edges will get poor. For bidirectional signals you'll definitely want actual chips doing the thing. And for power rails you need ...
by TmEE co.(TM)
Wed May 23, 2018 9:31 pm
Forum: Megadrive/Genesis
Topic: Color analysis between different emulators/editors
Replies: 5
Views: 585

Re: Color analysis between different emulators/editors

The video DAC part is figured out pretty much. There's 17 taps on a long resistor structure and each tap is turned on with a control signal to enable certain level on the color channel output. 15 MD mode levels plus two SMS mode exclusive levels.
by TmEE co.(TM)
Thu Apr 26, 2018 6:17 pm
Forum: Megadrive/Genesis
Topic: Struct maros/syntax and naming conventions
Replies: 6
Views: 642

Re: Struct maros/syntax and naming conventions

I do stuff like that :

OffsetName EQU 124

MOVE.W OffsetName(A0), D0

EDIT: Exactly what you try to avoid... lol. I don't know of any better solution.
by TmEE co.(TM)
Wed Apr 04, 2018 6:30 pm
Forum: Megadrive/Genesis
Topic: Game loops and Vertical Blank interupts
Replies: 29
Views: 1592

Re: Game loops and Vertical Blank interupts

I poll for VBL bit in the VDP in main loop and I also set a flag in the frame interrupt. If main loop sees that the flag is set after all game logic it can assume slowdown has happened and act upon it, when flag isn't set the logic ended before frame did.