Figuring out how the Sega DS-16 interfaces with the Genesis.

So I pulled my DS-16 out today and decided to investigate it. Trying to figure out how it interfaces with a Genesis. Figured it out for the most part thanks to some pinout diagrams.

Here are the pinouts of both the expansion port and cartridge slot on the Sega Genesis:

Cartridge slot:



Expansion port:



Now this is where it gets interesting. The expansion port shares the same address lines as the cart slot save for the last 6 A lines. Address lines A18 through A23 are only on the cart slot. I traced the DS-16 out on the expansion connector and found that pins A03 through A20 connect up as well as pins B03 through B22. They all connect for the address lines as well as whatever B21 and B22 do on the DS-16. pins A28 and B28 connect as well but that's for power to the DS-16 itself. Since address lines A18 through A23 are missing from the expansion connector they have to be pulled from the cart slot. confusing is the fact A29 and B29 are hooked. Why does the audio need to be hooked?

A look inside the dummy cart showed 2 chips, capacitors, resistors, and a voltage regulator. A look at the connected pins shows pins B06 through B11 hooked giving us our missing address lines A18 through A23. B02 is connected and I think that is the reset signal. when you switch a game the console resets and this must be done through B02. B17 is hooked and that is !C_CE. I think that's chip clock enable. Makes sense since the unit has a bunch of discrete logic chips and such in it. B30 is hooked straight to the +5v lines at A02 and A31. B32 is hooked straight to ground for the cart detection. A01 and A32 are hooked to GND. Lastly is pin B31. I still don't know exactly what this does but it is hooked straight to one of the chips in the dummy cart.

So I now know how all the lines are connected and what most of them do. I'm just confused by expansion port B21, B22, A29 and B29, and cart slot B30 and B31.

Here's a list and number of all the chips on the system itself. I'll try to make a diagram showing how it's all hooked up sometime in the future. May help towards homebrewed jukebox systems for this machine. I won't bother with the capacitor values or resistors since there are so many...

Dummy cart:
1x NEC D560 K31S regulator
2x 20 pin HD74HC244P chips
A few resistors and capacitors

DS-16 unit itself:
1x 17805 regulator
1x 8 pin NE555C on the auto switch timer side
12x 20 pin PC74HC245P. 10x are 845110T Hnn9249PC and last 2 are 818500T Hnn9223PC
1x 14 pin PC74HC00P

All the rest are 16 pin chips:
7x white chips probably made from ceramic. Part # BI 898-3-R100 9247
2x HD74HC138P 2M4T
1x HD74HC138P 3B36
1x PC74HC161P 757500T Hnn9223PA Y
1x HD74HC251P 3A1T
1x HD74HC02P 2L15
1x HD74HC14P 2M16

That's all aside from numerous capacitors, resistors, resistor arrays, a pot for the auto switch time adjustment, and a transistor.

Hope this helps you guys. I'll see about working on making a diagram of the whole thing sometime. It'll be gigantic due to all the traces, parts, and cart slots.

 

The logic gates explain everything.

 

x

 

I'll go to the forum and put this up. Maybe someone there will know something.

As for pictures, ask and ye shall receive. sorry if they're a bit blurry. Camera doesn't have a macro mode...








I'll still be working on a complete diagram of the wiring since I can see it all and what I can't see under the chips shouldn't be too hard to trace with a meter.

 

x

 

I assume it's only using some bus switches and there your're ready to go with the use of multiple carts.

 

The logic gates are probably what is selecting the cartridges. 6 cart slots means you only need 3 bits to control things and have two slots available for later. Drawing out the entire schematic isn't necessary and you can derive a good chunk of it by figuring out just one slot.

 

I looked back over the pinouts and found something interesting. All the pins used on the expansion port minus A29 and B29 are also on the cart slot. I traced those 2 and they seem to be hooked directly to somewhere on cart slot 5. Don't know if they do anything or if it was some extra stuff left on the board. Remember, this thing is from 1989. The CD system came out 1991 so maybe these 2 pins did something else besides audio on the first model Genesis systems from 1989. Who knows.

I'm thinking the unit will still function with everything hooked to the cart slot only. I'll investigate that in the next few days. Gonna have to build some custom cables to pull it off but I have all the stuff to do so without having to modify anything on the DS16 itself. If it still works then that will be a step closer to reverse engineering this thing to make homebrewed versions. System would be much simpler if it worked through the cart slot only. Now to find my 60 pin Famicom cart slot, busted Famiclone game PCB, 64 pin Genesis cart slot, busted Genesis game PCB, and some IDE ribbon cable.

Still wonder why it doesn't work with SRAM games like Sonic 3. Must have left a certain pin off to prevent demo games from having stored data on them. Such a shame. Even the Everdrive MD has problems with it. The flashcart works as long as you don't try to access the SD card to flash a new game and the game already flashed doesn't use SRAM. Fails when I try to access the game list on the SD card. Gives me an Init fail error. That tells me a few address lines needed for this function as well as the SRAM save function are missing. If a reversed version is ever made that will have to be sorted out.

 

Hi, sonicdude,

As APE said, you just need to figure out the address decoding.

The 74LS138 chip is extremely common.
It pulls one of it's output pins low depending on a 3-bit address input (and 3 enable pins have to be in the correct state).

There is probably a latch / register too, or it's using the PC74HC161P counter for latching the cart number?

If you can get some much better photos of the boards, we could probably figure out the basics.
I know what it's like with the camera stuff - I've never had a really good camera which can do macro well, only a cheap Samsung, or my old HTC Desire cam.

If you can get some better photos - it's preferable to get them as square-on as possible.
What I usually do then is line them up in Paint Shop Pro as separate layers, flip the underside image, then you can hide / show the layers to trace the signals.

Shouldn't as tough as what I reversed recently from photos, that's for sure. lol


OzOnE.

 

Looks like IC20 to IC22 down the side are doing a lot of the cart port selection.
You need to trace the /CS signals from the cart slots, or whichever seem to be going to those individual vias to IC20,IC21,IC22 (mainly IC21 and IC22 by the looks of it).

I'm just looking for some clearer PCB photos, but I don't think there are many / any on Google?

Oh, I just read the wiki about it - pretty much suggests that the counter is in fact used as the main latch / counter for cart selection.
It's outputs probably then go to IC21/IC22.

Let me guess - is IC20 the 74HC161?

EDIT (again): btw, I can tell you what most of the 68K signals are for. That board image I posted was a 68K system as well, so I had to learn all about that CPU.
(It's the main CPU board from a Quantel Paintbox system which was owned by the BBC - used for things like Dr Who, Tripods, parts of Knightmare series 1, Weather, news etc.)

 

If you can get me some good PCB pics, I'm sure I could reverse it pretty quickly.

I'll do an Eagle schematic.

If all you want is a multi-cart switcher which uses an external button and resets the console, then that's fairly easy tbh.

 

I'll work on getting some cleaner pics in the next day or 2. I was mostly doing this to get some information on this device. The Genesis has been reversed up the wazoo so I figured information on this would be good for someone to mess with. I don't have the skills or tools to do it myself but I can get you all the info and pinouts on it to be reversed by someone with the skills and tools.

I bet if someone were to make this it would sell. Maybe not like the Everdrive flashcarts but more for someone with a retro game room or something. Could be used for a demo setup that auto switches the games like the original was used for in stores.

 

Yep, it's good to try to preserve all the info on these sorts of unit.
That's why I'm finding as much as I can on the Naomi too.

Don't worry - all I need are clear pics of the DS-16.

btw, the dummy cart just has two buffers in there, nothing much fancy.
It sounds like it doesn't switch all the cart address lines though, so there may be a restriction on the max cart size?

Although, if you're saying that most carts work, then it's probably OK apart from the SRAM carts?
Normally, all you'd really need is to assert the /CART_CS line for the chosen cart, with maybe a few buffers / transceivers for the addr / data lines.

It would make a nice addition to a game room actually.
I don't really collect carts myself, but it's a nice idea.

 

Not very cheap I see?

http://www.ebay.co.uk/itm/Sega-Gene...US_Video_Game_Controllers&hash=item3a866e92a5

 

Funny thing is I got mine for the same price from California and it came complete.

 

Great idea. But this one should be really easy to reverse engineer - it's all pretty straight forward (quite common parts). With some high res pics and the pinouts you can fix it within a few hours. Although if you design it I doubt you can make it really cheaper (the PCB board is quite big, and those headers...), but I want one ^^

 

Didn't expect my random musings to turn serious like this. (Damn. No more smileys to put here...)

I guess if people want it I'll work on some good pictures and a schematic. I'll still make the big ass schematic for this just in case I can't get good pictures to deduce the traces from. What I really need is to take some scans of the boards. Maybe grandma will let me use hers since I don't have a working scanner. Board will fit on the bed of hers with no problem.

First I get people interested in the DCIO project, I just randomly mess around with my DS-16 out of boredom, and people are interested in my findings. What's next? Getting a Nintendo M82 and reverse engineering it? LOL

Need to see about fixing the auto switch timer circuit. Doesn't seem to want to work right. Hoping it's just a capacitor. Gonna see about recapping the whole thing. shouldn't be too costly. Thing has only maybe 20 at most. Want that working so I can set it up with games and no controller for a simple background decoration when I do have people over on rare occasions.

 

Hi,

Is there a switch or jumper position anywhere for enabling / disabling the auto-switching timer?
I can't imagine the auto switch would be permanently enabled, so there was probably a way to disable it?

If it's based on the 555 (very likely, it's next to the twiddler pot), then yep, I'd change the caps around that first.

Pin 4 on the 555 chip (/RESET) needs to be above 0.7V before the timing will start.
Pins 6 and 7 are probably connected together. This is where the resistor / cap combination connects.

If you measure the voltage on pin 6, it should be very slowly rising.
The output is on pin 3, and gets pulled low when the voltage on pin 6 reaches 2/3 of the supply voltage.

It might be wired differently though, and I haven't worked with a 555 for many years.
Is it working at all, or not triggering? If the timing is unreliable, it could be a cap, but is far more likely to be the pot that's worn.

Don't worry about the schematic. I can probably trace most of it fairly quickly with clearer photos.
The Paintbox board I posted was a bit blurry (and resized), but the original size was enough to trace it.

 

If you look on the second and third picture you do see a switch on the right.
And around it you see the pot and below the switch it does indeed looks like a 555 with the big cap probably for the timing (also the amount of resistors seems about right for it to be a 555). I would say pretty good guess OzOne

 

To answer your questions. yes, the 555 is for the auto switch timer. Yes the switch next to it turns the auto switch timer on and off. Yes the white pot next to it is for adjusting the time before switching the games when it is active. I took some better pictures. Hope they will be more useful.