Discussion DreamCast R&D and Documenting

[Shank]

The dreamcast is probably the least documented console that can be portablized. While it is very unlikely that significant motherboard trimming could occur, documenting the console will be necessary to actually build portables. There are bits and pieces scattered on the internet, but no quality guides have been made. In this thread, we will try to accumulate the information from around the internet, share notes, and discuss findings and theories. The information found in this thread should not be taken as absolute, because, as of writing, the electrical side of the dreamcast is still not fully understood.

Main Voltage lines:
12v
-Not needed to boot
-Used by disc drive laser

5v
-Required to boot
-Uses .42a

3.3v
-Required to boot
-Uses 2.8a
-Powers the 2v and 2.5v lines
-Uses .4a when not feeding onboard linear regulators

Onboard Voltage Lines

2.5v
-Draws 1.6a

2v
-Draws .75a

I have found 2 onboard voltage lines, 2v and 2.5v. These are powered by linear regulators, fed by the 3.3v line. Powering these by custom regulators instead of onboard ones may lead to significant reduction in power consumption.

Other things to discuss:
Video options/pinouts. Aftermarket/fpga video options?
Disc drive replacement options and wiring diagrams
Controller diagrams
Source of/replacement for 2v and 2.5v lines
Booting without the fan attached
Can any components be removed?
Can we trim it? (probably not much if any)
Which components need what voltage
Datasheets for onboard off-the-shelf chips

Discuss!
Share your notes, findings, and diagrams. All discussion is encouraged.

 

[Morgan_The_Adventurer]

I'm actually working on a DreamCast Portable myself. I'm not doing any trimming since theirs no info on it and I know nothing about that sort of thing. But here are some things that I have figured out

Fan:
The older models with the metal fan have to be installed or else you'll need something to take its place (some kind of timer? I forgot not)
I believe newer systems can work without the fan plugged in.

Drive replacement:
I decided to use an the IDE drive mod and connect it to a CF card reader. I have to get a better CF card to test it more, but it looks like it works well for alot of games.
It does require a replacement BIOS chip in order to load right into the IDE drive
If you want to remove the Disk drive completely you'll have to install a crystal oscillator to bypass it

If you are removing the disk drive then you don't need the 12v

I'll post some pictures when I get home from work

 

[Shank]

It does require a replacement BIOS chip in order to load right into the IDE drive
If you want to remove the Disk drive completely you'll have to install a crystal oscillator to bypass it

Interesting. I've never seen any information on this. I'd love some more details on it.

As for the fan, there as got to be a way to spoof the fan on older models. RDC mentioned using a voltage divider, but I was unable to get that to work.

 

[Morgan_The_Adventurer]

Here's some good info on the IDE mod, they also talk about the BIOS mod as well.
http://www.theisozone.com/forum/viewtopic.php?f=144&t=53352&p=364015#p364015

The BIOS mod is mostly needed to load into DreamShell to load games from. But it can also used to make your system region free
http://www.mmmonkey.co.uk/sega-dreamcast-region-free-bios/

As for removing the GDrom you need an Active Crystal 33.8688 Mhz (I had to buy 10 when I only needed one, so if anyone wants any I'll be happy to sell it to you)
There was barely any information on this, this was the only website I found that helped.
https://translate.google.ca/transla...ress.com/category/sega-dreamcast/&prev=search

Also you might find this useful?
http://yam.20to4.net/dreamcast/va1.html

 

[Crazzyleprechaun]

Wow thats a lot of information I will be attempting the GDrom removal mod after I order one of those crystals

 

[cheese]

Wow thats a lot of information I will be attempting the GDrom removal mod after I order one of those crystals

Aren't they on the official drive already?

 

[Morgan_The_Adventurer]

Wow thats a lot of information I will be attempting the GDrom removal mod after I order one of those crystals

Just make sure you do the BIOS mod and IDE mod first (if your doing the ide mod anyways) you'll need the Disk drive to install the data on the new bios chip.

Aren't they on the official drive already?

The crystal on the drive doesn't seem to work by itself. Atleast I wasn't able to get it working. The one on the drive is different form the one I had to use to bypass the drive.

 

[Providencial]

On a break at work so here's some random stuff off the top of my head which could be useful to people:

Power:

I can totally confirm 12v is only needed for the disc drive. The console runs perfectly with a GDemu in place of the DD with nothing connected on the 12v rail.

I have seen the same reported by trusted peeps about the USB GD-ROM.
According to what I have read the main difference between the two in terms of power is that the GDemu uses the 3.3v line and the USB GD-ROM uses the 5v. I understand this is also why the GDemu doesn't work with any mobo revisions other than the VA1.

Many people have run the disc drive succesfully with 7.4v from li-ions instead of 12v

Console and controller boot and run fine if you only input 3.3v (i.e. no 5v or 12v), BUT if you plug in a VMU the controller stops responding.
(So you need 5v for peripherals, which is not unusual)

About controls:
It is well documented that the genuine controller uses hall sensors instead of pots for the analog stick and triggers. It is written in many places that for this reason you cannot use standard 5k pot stocks and triggers.
THIS IS NOT CORRECT: RDC wrote on modretro that simply removing the op-amps for the hall sensors (two small IC's) lets you hook up standard pots and I can 100% confirm this. I will post pinouts with alternative points when I can.

I am confident the official controller can be trimmed extensively, haven't yet taken the plunge but do have lots of sketchy hand-drawn pinouts I can make nice.

There are plenty of examples of people extending the VMU connections with IDE wire with no impedance problems, I will post my findings on this when I have experimented more.

The daughter board for the controller sockets is very simple (1 fusible resistor, 2 resistors, 1 coin battery for RTC and 1 LED) so can be removed and replaced with the components in a very small form factor.
I have a sketchy hand-drawn circuit diagram I could do up.

Some sources online suggest changing out the RTC coin cell with a normal CR2032 (or AA's), others point out this could be dangerous as the original is rechargable. The rechargable one is basically impossible to find available as far as I can tell. A common work around is replacing the resistor preceding the cell with a small diode to stop current flowing into the cell to be able to use the commonly available CR2032.

I will do a write-up about game loading options with pros and cons soon.

 

[Providencial]

About the fan: As far as I can tell all the VA1's (most common board revision) have the three-wire fan which requires a that the mobo recieves a signal or else the whole system cuts out after a few seconds. This I can confirm with my own experience.

The original fan is relatively small 30mm, but quite noisy.

A different 3-wire fan should work but I can't confirm personally.
Or here's a good tutorial on using a small 555 timer IC to replicate the signal https://www.google.cl/url?sa=t&source=web&rct=j&url=http://randomprojectman.blogspot.com/2008/05/even-though-its-pretty-dated-system-i.html?m=1&ved=0ahUKEwi8ppauw_XTAhXLEJAKHUXVBDAQFggcMAA&usg=AFQjCNH_Smzl1d5CLs__HLtGipl84VcALQ&sig2=HNXMbEUk4E4w5eycjAihnQ

Then you can use any fan (or none at all).

 

[Providencial]

Also have to say it's great to hear there's another DC portable in the works @Morgan_The_Adventurer !

We want a thread with pics!

(Lets get enough action to warrant a Sega/DC section on BitBuilt!)

 

[Providencial]

P.S. does anyone actually have a DC that is not revision VA1?

I have 3 mobos currently, all US/NTSC, but have also owned a few PAL models in the past and have never actually seen a VA0 or VA2.

 

[Doom]

Post to remind myself to look at my dreamcasts this weekend for revision notes.

Also calling the original dc fan "quite noisy" is def an unterstatement.

 

[Crazzyleprechaun]

I have only seen VA1 revisions as well I could also make some pin diagrams if you guys want any for future reference just simple ones like for av and the controller

 

[Shank]

P.S. does anyone actually have a DC that is not revision VA1?

Both of mine are VA1

(Lets get enough action to warrant a Sega/DC section on BitBuilt!)

Totally. I'm sure we could if we have enough to show. The pipe dream would be to accomplish enough to warrant @Aurelio porting GC+ over to DC+
@Providencial and @Morgan_The_Adventurer good stuff guys, keep it up! Im gonna need to do some reading and catch up. You seem to have more knowledge on it than I do. I'm going to look into the voltage and electrical side, and see how much more efficient we can make it by running custom regs on the onboard voltage lines.

How "hackable" is the software part of the dreamcast? Is it like the wii where you can actually mess with stuff, or stuck the way it is like the gamecube?

Also, paging @Herma, because you said you were interested in dremcast progress at MGC.

 

[Morgan_The_Adventurer]

Also have to say it's great to hear there's another DC portable in the works @Morgan_The_Adventurer !
We want a thread with pics!

Lol I've been writing stuff up and taking some pictures to get ready for a thread. Ill probably take some more pictures and show off what I have so far.

P.S. does anyone actually have a DC that is not revision VA1?

I'm also using a VA1. But I have seen others.


It's great to see some interest in DC modding! This will be a huge help for when I work on the parts I'm not so sure about.

 

[Herma]

I've got some documentation on the GD-ROM, was gonna start doing some stuff but real life and girlfriend and such seems to be taking up more time than I expected. I'll get to it eventually, though I am interested in seeing things done.

My primary focuses in any sort of Dreamcast information in general are: GD-ROM, Expansion port (esp the NIC), and karaoke.

 

[Aurelio]

The pipe dream would be to accomplish enough to warrant @Aurelio porting GC+ over to DC+.

Send me a DC (an hackable one would be ideal), a controller (maybe with a vmu as well if you're interested in emulating that as well) and a game to test everything with and I might start doing some work on it

 

[Shank]

Send me a DC (an hackable one would be ideal), a controller (maybe with a vmu as well if you're interested in emulating that as well) and a game to test everything with and I might start doing some work on it

Sounds like a deal. I'll add that to the list of things I'm sending you.

 

[Providencial]

How "hackable" is the software part of the dreamcast? Is it like the wii where you can actually mess with stuff, or stuck the way it is like the gamecube?

It's like the gamecube.
There is a UNIX-like OS called Dreamshell (referred to as "DS" from now) which is similar to Swiss on the GC.

You can run DS from a burnt CD-R, and use it to run games, homebrew or apps from an SD card or IDE HDD.

SD requires a serial port to SD card adapter (you can build one simply or buy from China).
IDE HDD is the same: many people have made QSB/plug-n-play solutions or you can hand-solder it.

As @Morgan_The_Adventurer mentions you can fit a replacement, home-flashed BIOS and this allows the DS image to boot from SD or IDE. Then you can remove the disc drive if you spoof a signal with the right crystal.

SD loading is balls slow, with not great compatibility and you have to use ISO's in a special format (not the standard rips)

IDE HDD loading is better in all respects, but still not perfect. (Eg. Rez and a few other key games still don't work, CDI, the most common disc images available aren't fully supported etc.).

The IDE HDD mod is known as "G1-ATA".
G1 is the disc drive port on the DC, and ATA is what people used to say for IDE.

DS has other features apart from just loading stuff (file explorer, disc ripper, console region changer etc.) and is often the simplest way to transfer/backup VMU save files.
It is made by an epic russian hacker called "SWAT", and there's a forum which has enough stuff in English.

There are other custom BIOS images (google "japanese_cake" for example) which do other neat things.

I will make a big pro's and con's table with all the game loading options! (there are like 7...)

 

[Herma]

There is an SD card GD-ROM replacement in existence. I can link when I'm not at work. But I think it's called GDEMU.

Iirc the GD-ROM protocol is just PATA and like an explicit ripoff of CD standards with some extra stuff slapped on. In the document I have it's obvious they used a CD protocol document as a template because they don't even bother changing CD-ROM to GD-ROM in most places.