Welcome to Obscure Gamers

Join us now to get access to all our features. Once registered and logged in, you will be able to create topics, post replies to existing threads, give reputation to your fellow members, get your own private messenger, and so, so much more. It's also quick and totally free, so what are you waiting for?

[DEV] : MOD Dreamcast REV0 (Va0) with GDEMU

Xrider

Registered
Registered
Joined
Apr 19, 2020
Messages
31
Reaction score
54
Points
18
AG User Name
Xrider
AG Join Date
19/05/2020
Hello,

Just a little message to let you know that the Dreamcast Rev0 curse (Va0 motherboard) with GDEMU has been lifted for the first time, and the mod is MADE IN FRANCE
Yes, this is a world first to my knowledge

Small video:
http://delta.island.online.fr/partage-darius/Dreamcast-Rev0-GDEMU/IMG_2964.MOV

The Techniques:

The Va0 (Rev0) motherboard has a logic level of 5V on the G1 bus

On this G1 bus of the Va0 we find:
- The GDROM (logic level and 5v power supply)
- The Bios (logic level and 5v power supply)
- Flash memory (logic level and 5v power supply)
- Holly, the Dreamcast GPU (5V and 3.3V tolerance)

The other motherboards of the following revisions (Rev1 and Rev2) work with a 3.3V logic level on the G1 bus
The GDEMU was designed for the Rev1, they represent the vast majority of Dreamcast

On this G1 bus of the Va1 we find:
- The GDROM (logic level and 3.3v power supply)
- The Bios (logic level and 3.3v power supply)
- Flash memory (logic level and 3.3v power supply)
- Holly, the Dreamcast GPU (+3.3V and +5V tolerance)

Here is an extract from the Dreamcast service manual representing the G1 bus:





To do this, here are the components to use:

BIOS: MX29LV160
FLASH: MX29LV002

It will therefore be necessary to unsolder these two components and pre-program the two memories (MX29LV160 with a bios, I recommend Japanesecake 1.02 https://japanese-cake.livejournal.com and the MX29LV002 with the dump of your old flash memory).

Then you have to install the two components, lift the power pins, and connect them to a 3.3V point (and yes, otherwise they will take 5V and they will not like ... lol)

Then on the front of the CM, remove component D503 and make a strap:



Good news, region changer now works on Rev0 without adding a shunt or anything else!

WARNING :
The original 5V GDROM reader will be incompatible after modification!
Use only the GDEMU or a 3.3V reader found in the Rev1
 
Last edited:

darcagn

AG Refugee
Refugee
Registered
Joined
May 30, 2019
Messages
144
Reaction score
181
Points
43
Location
Louisiana
Website
dcemulation.org
AG User Name
darcagn
AG Join Date
May 12, 2007
Good news, region changer now works on Rev0 without adding a shunt or anything else!

This is not a good idea to be left like this, as software may write to the flash and brick the console. The Sega DC checker software for example clears the flash and will also clear (and brick the console) factory region coding if this mod has been performed. I don't know how widely used it is, but I myself do use it to check DC consoles I handle. Other software may do it too

MX29LV002 supports protecting specific sector ranges just like the original DC chip does, might be better to wire it up to protect the 8K partition 0 at $1A000 if it is possible
 

FamilyGuy

2049 Donator
2020 Donator
2019 Donator
Refugee
Registered
Joined
May 31, 2019
Messages
295
Reaction score
298
Points
63
AG User Name
-=FamilyGuy=-
AG Join Date
March 3, 2007
The Sega DC checker software for example clears the flash and will also clear (and brick the console) factory region coding if this mod has been performed.
My dead Dreamcast can confirm this.
 

megavolt85

DreamShell Developer
Refugee
Registered
Joined
Jun 17, 2019
Messages
147
Reaction score
408
Points
63
Location
Russia
Website
www.dc-swat.ru
AG User Name
megavolt85
AG Join Date
01.09.2015
Holly, the Dreamcast GPU (5V and 3.3V tolerance)

as a rule, such microcircuits have separate power inputs for the core and the bus
you just changed what is connected to the G1 bus, but I do not see any changes in HOLLY

if DVCC HOLLY remained connected to +5V, then you made it worse with your modification
it was much easier to do like all manufacturers of flash cartridges for MegaDrive, to replace all resistor assemblies from 33 ohm to 100 ohm
 
Last edited:

Xrider

Registered
Registered
Joined
Apr 19, 2020
Messages
31
Reaction score
54
Points
18
AG User Name
Xrider
AG Join Date
19/05/2020
as a rule, such microcircuits have separate power inputs for the core and the bus
you just changed what is connected to the G1 bus, but I do not see any changes in HOLLY

if DVCC HOLLY remained connected to +5V, then you made it worse with your modification
it was much easier to do like all manufacturers of flash cartridges for MegaDrive, to replace all resistor assemblies from 33 ohm to 100 ohm
Hello megavolt.

i confirm, holly work at 3.3v on VA0
Check this (All VCC input is +3.3V):

ofcourse, holly accept +5v and +3.3v on g1 bus.

You can see the datasheet spec from sega "+5V Tolerance" on Holly G1 BUS
 
Last edited:

Xrider

Registered
Registered
Joined
Apr 19, 2020
Messages
31
Reaction score
54
Points
18
AG User Name
Xrider
AG Join Date
19/05/2020
This is not a good idea to be left like this, as software may write to the flash and brick the console. The Sega DC checker software for example clears the flash and will also clear (and brick the console) factory region coding if this mod has been performed. I don't know how widely used it is, but I myself do use it to check DC consoles I handle. Other software may do it too

MX29LV002 supports protecting specific sector ranges just like the original DC chip does, might be better to wire it up to protect the 8K partition 0 at $1A000 if it is possible
Hello,

Don't worry about this :-D

Your console can boot if the flash is dead with Japanesecake 1.02 https://japanese-cake.livejournal.com
No black swirl of dead or other thing...

And good new if the content of your flash is out...
Our friend "Dragoncity" have software solution for fix this :
Chapter 4.5.3 – Black Swirl of Death
 

megavolt85

DreamShell Developer
Refugee
Registered
Joined
Jun 17, 2019
Messages
147
Reaction score
408
Points
63
Location
Russia
Website
www.dc-swat.ru
AG User Name
megavolt85
AG Join Date
01.09.2015
i confirm, holly work at 3.3v on VA0

in this case, the BIOS can not be changed, it will work fine if it is powered from +3.3V
and the flashrom will have to be replaced, because when the power supply is 3.3V, there may be problems with writing

MX29LV002 supports protecting specific sector ranges just like the original DC chip does, might be better to wire it up to protect the 8K partition 0 at $1A000 if it is possible

it is possible, it can be done even by the dreamcast itself
 

madsheep

Registered
Registered
Joined
Jun 26, 2019
Messages
5
Reaction score
3
Points
3
AG User Name
madsheep
AG Join Date
Jul 19, 2013
i don't know about electronics but wouldn't be more easy to mod the gdemu? with voltage regulator/filter or something?
 
Top