Search found 2318 matches

by TmEE co.(TM)
Mon Oct 15, 2018 3:06 pm
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 639

Re: Bus Arbiter and IO Chip Access

EDCLK generation is made with a little sub board on MD1 VA0 that consists of 3x logic chip. IA14 is probably made by the 00 chip between the RAMs on VA0. Nobody seems to have made a schematic of the board yet though. Full EDCLK pattern is "8aaaaaaa99aaaaaaa8aaaaaaa99aaaaaaa" where each symbol is one...
by TmEE co.(TM)
Thu Oct 11, 2018 9:18 am
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 639

Re: Bus Arbiter and IO Chip Access

EDCLK is an input to the VDP. And now I actually remembered that it is the HSYNC that was the problem. Because of the open drain factor I had problems with my first set of measurements as probe capacitance caused my measurements to be off by several pixels due to rise of the signal getting altered. ...
by TmEE co.(TM)
Thu Oct 11, 2018 6:57 am
Forum: Sound
Topic: YM2612 clock stopping
Replies: 3
Views: 215

Re: YM2612 clock stopping

I only have SE-95 clone chips to test, I haven't tried it though.
by TmEE co.(TM)
Thu Oct 11, 2018 6:55 am
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 639

Re: Bus Arbiter and IO Chip Access

EDCLK is open drain, you need a pullup on it.
EDIT: It isn't, but HSYNC is and it is used for EDCLK generation by the Bus chip and it caused me trouble. More details in next post by me.
by TmEE co.(TM)
Thu Oct 11, 2018 3:03 am
Forum: Sound
Topic: YM2612 clock stopping
Replies: 3
Views: 215

YM2612 clock stopping

When you stop the clock of YM2612 it needs to settle in Low state or the chip will get burning hot within 10 seconds or so. I have a project where the clock can be stopped and I noticed the chip getting unusually hot in very short amount of time when the clock was stopped in High state.
by TmEE co.(TM)
Wed Oct 10, 2018 5:23 am
Forum: Megadrive/Genesis
Topic: Cart Design Questions
Replies: 26
Views: 1583

Re: Cart Design Questions

Low and high bytes contain same data when doing 8 bit writes.
by TmEE co.(TM)
Tue Oct 09, 2018 4:58 pm
Forum: Megadrive/Genesis
Topic: simple 68k loop
Replies: 17
Views: 375

Re: simple 68k loop

What is that DC.L doing there ? It will be executed as an instruction which will depend on exact value of _INT.
by TmEE co.(TM)
Thu Oct 04, 2018 12:09 pm
Forum: Hardware
Topic: Second Dimension PCB's
Replies: 6
Views: 385

Re: Second Dimension PCB's

EPROMs are no more permanent than NOR Flash. Both work on same sort of principle and will degrade in same sort of manner. EPROMs will last less though, 50 years is probably the maximum while most chips I have looked at give 40 year rating. NOR flashes are usually rated for over 100 years.
by TmEE co.(TM)
Tue Oct 02, 2018 12:38 pm
Forum: Hardware
Topic: Second Dimension PCB's
Replies: 6
Views: 385

Re: Second Dimension PCB's

PCBs aren't a problem, main thing is EPROMs. You can mostly only get pulls, meaning they're been used before and their state is often unknown. Those chips haven't been produced for many years now and eventually the supply will run out, leaving dodgier and dodgier parts left until those are gone too.
by TmEE co.(TM)
Mon Oct 01, 2018 8:10 am
Forum: Megadrive/Genesis
Topic: IO access differences in MD mode vs SMS
Replies: 4
Views: 198

Re: IO access differences in MD mode vs SMS

Since it would require bus crossing, abitration will take place and one will wait while other finishes, there will not be a bus conflict happening.
by TmEE co.(TM)
Thu Sep 20, 2018 4:37 am
Forum: Sound
Topic: Regarding the YM3438 on the Mega Drive...
Replies: 11
Views: 600

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: 600

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: 30
Views: 1923

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: 26
Views: 1583

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: 26
Views: 1583

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...