Search found 2322 matches

by TmEE co.(TM)
Fri Nov 23, 2018 4:06 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 329904

Re: New Documentation: An authoritative reference on the YM2612

It is possible to update DAC once every sample if you have cycle synchronity to the YM. I did some tests where YM and Z80 were made to share the clock in MD and I could get unique samples out every 144 cycles. Doing rates between full and half sample rate are very ugly though due to the "resampling"...
by TmEE co.(TM)
Sat Nov 17, 2018 9:59 pm
Forum: Hardware
Topic: Controllers and wrong I/O pin directions
Replies: 9
Views: 715

Re: Controllers and wrong I/O pin directions

That resistor is the same as 330ohm to ground if it connects to another output, kind of like both outputs driving to a 330ohm load if their states differ (one side high, other low and vice versa). It is a current limit and roughly like lighting up a LED via an IO pin. I'm sure the IO port output dri...
by TmEE co.(TM)
Mon Nov 12, 2018 4:26 pm
Forum: SGDK
Topic: An error check in the 3 line handshake
Replies: 12
Views: 634

Re: An error check in the 3 line handshake

There are 330ohm series resistors on TH and TL or TR lines which will help in cases using those pins out of the normal way. 330 ohms isn't a huge load to fight.
by TmEE co.(TM)
Mon Nov 12, 2018 3:24 pm
Forum: SGDK
Topic: An error check in the 3 line handshake
Replies: 12
Views: 634

Re: An error check in the 3 line handshake

Pins on the controller port can be both inputs and outputs and some devices expect the direction to be set different from what a normal controller configuration uses. If two outputs get connected together you will have one or both sides getting damaged sooner or later.
by TmEE co.(TM)
Mon Oct 15, 2018 3:06 pm
Forum: Megadrive/Genesis
Topic: Bus Arbiter and IO Chip Access
Replies: 25
Views: 1571

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: 1571

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: 1031

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: 1571

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: 1031

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: 2246

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: 21
Views: 1752

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: 1277

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: 1277

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: 481

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: 1068

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.