Dreamcast Modchip & Bios replacement thread

[Link83]

Hi everyone,
(Before I go on, I realise that 'backups' dont require a modchip, and that there is now a mod that allows you to change you Dreamcasts region, but I am really only interested in making a 'region free' console, which so far means it has to be a modchip)
I have recently bought some Dreamcast modchips but am having great difficulty wiring them up and getting them to work at all 
I had previously used ones that came on a nice little PCB, heres a pic:-

This one works great, but I havent been able to find a cheap supplier who still sells them anymore 

The only Dreamcast modchips I could find that were still available are the 'chip only' ones (no PCB), but I figured "that shouldnt be a problem", so bought a few of them  Heres a pic of one:-

I have tried to wire them up loads of different ways but still cant get them to work 

There are so many different wiring diagrams for the 4/5 wire Dreamcast mochips that I am totally lost as to whats the 'correct' way to wire them. Heres some different guides I have found on how to install the Dreamcast modchip:-
http://web.archive.org/web/20030424000008/http://www.maxking.co.uk/dreamcastmod.htm
http://www.kreidler.be/Shinebi/dreamcast%20modchip.htm
http://www.joystick.it/dre/dream5ok.htm
http://www.hardcore-gamer.net/tienda/images/instalacionchipdreamcast.jpg
I have tried pretty much all of the different ways shown but they still dont work.

The different wiring schemes are not helped by the fact that there appears to be a number of manufacturers of the 4 wire chips, like these:-
]

All use different programmable chips!

----------------------------------------------------------------------------------------------------------------------------
On a slighty different note, I am curious as to why the 4 wire modchip no longer supports 'warm booting' of games (eg from the menu) when previous Dreamcast modchips did.

I find it curious that the 4 wire modchip I first bought has a small PCB with 4 extra soldering points on the board which are unused. What I wondered is could these points have been used to make an 8 wire (or less) modchip which supported warm booting?

Heres a pic of both side of the chip I am refering too, and on the third picture I have painted in all the circuit lines so you can see how it is wired:-



There is also this chip which is totally different to the ones commonly available elsewhere, and this one also apparently supports warm booting, but the company no-longer replies to emails:-
http://www.massystems.com/DC-Mod.html

Lastly, theres a 5 wire modchip that was sold by NCSX and used a totally different wiring scheme, lifting up leg 28 on the bios chip and connecting to both the pad and pin, I wondered if this 'pad and pin' method is what allowed warm booting?:-
http://web.archive.org/web/20030303223438/www.ncsx.com/ncs020700/ncs-dcmod-2-va1.htm

Thanks in advance for any help 

[l_oliveira]

A 2mb flashrom and a patched bios do the effect. Instructions on the rom patching can be found on another thread at this forum.

[Link83]

A 2mb flashrom and a patched bios do the effect. Instructions on the rom patching can be found on another thread at this forum.

Thanks for your reply 

I managed to find a thread saying how to hex edit the bios to be region free, but it didnt really go into detail on how to flash the new bios to the chip.

Is the original Sega Bios chip re-programmable? and if so can it be flashed 'in-system'?

If not I guess this method would require removing and replacing the original bios chip? - I think that may be alittle beyond my soldering skills at present 

Do you think it would be possible to make a 'homemade' Dreamcast modchip?

<EDIT> After having a look at the bios chip again I feel abit more confident that I could actually do it. What would be the exact Flashrom chip I would need?

I have had a look through AMD's site and have found a few 2MB Flashroms in 44pin SOP packages (which I think is the correct type?), but there is all sorts of other choices such as speed, 'boot sectoring', and voltage (3v, 5v) etc for each type of chip. If you could help me find a 2mb Flashrom chip that would be an exact replacement, and a programmer, I would very much appreciate it 

[l_oliveira]

The ROM on the Dreamcast uses a pinout similar to the 27C160 (JEDEC standard pinoout) and it's read in the 8 bits mode. (The chip is capable of both 8 and 16 bits output)

Which in turn is the *same* pinout as a Mega Drive ROM chip.

Any parallel 2 megabyte flashrom should work. In my case I used a 48 pin TSOP flashrom from AMD with an adapter for 44 pin SOP.
Since it will never get written to, you don't need to bother about pages and write protection mechanisms. All it need is to be 8 bit compatible and you can rewire it to the Dreamcast motherboard.

I did choose the AMD 48 pin TSOP because as you could see on the picture I had a adapter which made it a drop in replacement to the original ROM. But honestly you can use any 2MB memory as long you are able to program it with the patched Dreamcast bios.

[Link83]

Thanks for the reply.
I have never attempted anything like this before, but I am willing to learn and would love to be able to do this, so please forgive me if I ask any noob questions.

I think I have narrowed the chips choices to either a:-
AM29LV200B which is 3v
or the
AM29F200B which is 5v
Not sure which voltage is correct for the Dreamcast?

Also, there is a number of other letters for different options available which i could do with knowing, page 9 of this pdf shows what I mean:-
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/21526.pdf

Also, I would need a cheap programmer to write the Dreamcast Bios to the chip - any idea which one would be best?

If I managed to do this I would be happy to help anybody else who wanted to do it, or write a guide on how to do it - Unless you would consider doing this l_olivera?

Thanks again 

[l_oliveira]

You definitely want to use the 3v part since that's the voltage the Dreamcast operates with.

If you get the version which has the same package as the original mask ROM it's a drop in replacement.

And besides the patching information and a programmer you don't need much more information besides how to solder a SMD chip.

And I don't have enough patience for writing a tutorial but I don't mind replying any doubts you have so post them.

[Link83]

Thanks for your help 

Ok so I need the AM29LV200B
The only other chip options I could do with knowing is the 'Speed Option' and the 'Boot Code Sector Architecture'
The options are:-

SPEED OPTIONS
55R
70
90
120

BOOT CODE SECTOR ARCHITECTURE
Top Sector
Bottom Sector

I cant quite make out on your pictures what the code is on the chip you used for the mod - is there any chance you could tell me?

Also, I am looking into the cheapest/best programmer for this type of chip, and am currently looking at the Willem Programmer here:-
http://www.sivava.com/buynow.php?pd=A041

But I am not sure if I need this PSOP44 adaptor:-
http://www.sivava.com/buynow.php?pd=B09
or this PSOP44 adaptor:-
http://www.sivava.com/buynow.php?pd=B15

Does this seem like a good option? I dont know if Willem Programmers are any good, or if they would even work with the AM29LV200B as it is 3v, and the adaptor only mentions compatability with the 5v AMD chips.

Or is there any other cheap programmer you would recommend? This is the first time I have ever attempted something like this so any help would be much appreciated

I would even be interested in just buying pre-programmered Flashrom chips if anyone has the appropriate programmer and adaptor?

[Tiido Priimägi]

As for chips, boot sector does not matter, and I think 70ns or 55ns one is ok, maybe 90ns one is too.

[honeymustard]

Not sure if its any help, but I have a PAL DC, which I flashed to NTSC-U and 60Hz, and it seems to load PAL (Rez), NTSC-U (SA1+2, HOTD2, Crazy Taxi etc etc) and NTSC-J (Ikaruga), without having to be changed in anyway.

[Link83]

As for chips, boot sector does not matter, and I think 70ns or 55ns one is ok, maybe 90ns one is too.

Thanks  I think i'll go for either the AM29LV200BT-55RSC or the AM29LV200BT-70SC, just looking for a decent cheap supplier now.
I Still need to find a suitable cheap-ish programmer though if anyone could advise?

Not sure if its any help, but I have a PAL DC, which I flashed to NTSC-U and 60Hz, and it seems to load PAL (Rez), NTSC-U (SA1+2, HOTD2, Crazy Taxi etc etc) and NTSC-J (Ikaruga), without having to be changed in anyway.

Really? Do you have any other PAL games to test? (I read somewhere that some early copies of PAL Rez didnt have region coding) Are you sure there isnt a modchip fitted in your Dreamcast? If not I would be interested in knowing what Bios version you have (and possibly a dump?) if its not too much trouble.

[ken_cinder]

Easiest I could come up with, was found on this page. http://www.chipstar.ru/eng/products/index.htm

Chipstar Turbo @ $180 - http://www.chipstar.ru/eng/products/chipstargm.htm

And a 44 pin SO adapter - http://www.chipstar.ru/eng/products/adapters.htm#so44

Not saying that is what you should go with, just an idea of what you're looking at and will need.

[hotwater9]

Hello, I hope you don't mind me adding fuel to the fire but I just bought a 4 wire mod chip that is on a PCBA and I am trying to install it. Unfortunately my Dreamcast PCBA looks different than all of the pictures shown in online how-to installs. Here is a picture of my PCBA: http://gotfrogs.com/images/MyDreamcastPCBA.jpg

Do any of yo know how to install the chip on this PCBA revision or know of any instructions that provide a wiring diagram?

[Tiido Priimägi]

You've got the 3rd model... 3 wires can be hooked up with no trouble (VCC, GND and one wire that goes on the BIOS chip (MPR-21931-X2) but the 4th one will require some research, and photos probably won't do in this case...

[Link83]

Thanks for everyones help - I havent given up on this, im just saving up for a suitable programmer.

Can I just ask though, im trying to edit the bios as l_oliveira suggested:-

Better yet, take the vanilla DC bios (Dump from MPR21931 that is used with emulators  md5-128: E10C53C2F8B90BAB96EAD2D368858623)
and hexedit this :

00000510   72 C4 07 C9 03 66 05 E1  1D 40 0C 34 0C 35 1E B0   r?.?.f.?.@.4.5.?

into this :

00000510   72 C4 07 C9 03 66 05 E1  1D 40 0C 34 0C 35 08 A0   r?.?.f.?.@.4.5.

Basically change 1E B0 at 51E/51F to 08 A0.

And you hacked the bios.

Put it back into a flash chip, solder it to the dreamcast and happy playing

But I cant seem to find that string in the bios to change it 
I have the exact same MPR21931 with matching hash. What am I doing wrong?

Lastly, does anybody know where I can buy a SOP44 socket adaptor so that I can easily take the chip in and out of the Dreamcast for flashing?

[viletim]

Lastly, does anybody know where I can buy a SOP44 socket adaptor so that I can easily take the chip in and out of the Dreamcast for flashing?

I haven't bee inside a dreamcast for a while and don't remember how much breathing room there is... Would a there be room to stuff a DIP or PLCC flash + socket in there? SOP pads arn't too small, you could solder wires to them. Would save a money on programmer adaptors, fancy sockets, etc

[Tiido Priimägi]

PLCC chip won't fit in the area where the BIOS chip is, there's less vertical room as heatsink is there... DC is pretty packed up...

[Link83]

Thanks for the replies 

PLCC chip won't fit in the area where the BIOS chip is, there's less vertical room as heatsink is there... DC is pretty packed up...

This would just be for a test system - not a permanent solution, so there should be room if I either leave the shielding off or cut a hole in it over the chip

I haven't bee inside a dreamcast for a while and don't remember how much breathing room there is... Would a there be room to stuff a DIP or PLCC flash + socket in there? SOP pads arn't too small, you could solder wires to them. Would save a money on programmer adaptors, fancy sockets, etc

The wire idea would be a viable option, but I would still like a socket connected to the wires for easy removal/insertion - I dont fancy soldering/de-soldering all 44 pins every time 

Every time I search for a 'SOP44 socket' I end up finding expensive socket adaptors for chip programmers - not really what im after!

[viletim]

Every time I search for a 'SOP44 socket' I end up finding expensive socket adaptors for chip programmers - not really what im after!

Programming adaptors are the only mass market application for these sockets.

Have you tried Farnell and RS Components?

[Link83]

Programming adaptors are the only mass market application for these sockets.

Have you tried Farnell and RS Components?

Thanks for the suggestion, but I have tried both but cant seem to find anything 

...However, with another google search I managed to find this:-
http://www.chip-service.de/product_info.php?language=en&info=p190_PSOP44%20Sockel%20Yamaichi.html
Not cheap, especially once you add shipping - but probably the only one l I will ever find at this rate. Im abit concerned by the datasheet mentioning a maximum of 10 insertions though!

It seems to be the same/similar socket design to the one used by 'bITmASTER' here:-
http://www.fuzzymuzzle.com/Bitmaster/DC_Boot_ROM_Replacement.htm

I dont really fancy soldering over the top of the original bios chip as done here (half way down page):-
http://cadcdev.sourceforge.net/hdwrprj/navi/

Perhaps I will just solder and re-solder the bios chip each time - even if I ended up destroying the Dreamcasts motherboard in the process it would still be cheaper to buy another faulty Dreamcast (usually they just need the lasers pot tweaked) than to buy the above PSOP44 socket!

[Tiido Priimägi]

I think I would piggyback the new BIOS over old one myself... this way I can switch between the 2 if needed

[Link83]

OK sorry to bump this thead somewhat, but I would really appreciate some help 

I am currently in the process of putting a new 2MB bios chip in my Dreamcast. My plan is to solder it over the top of the old bios (Piggyback) as I couldnt find a socket cheap enough anywhere. Obviously I will need to have a switch to swap between the two, and from looking at the picture on this page:-
http://cadcdev.sourceforge.net/hdwrprj/navi/
I think I will need to have a switch on leg pin 12?

My concern is he also makes mention of needing to connect the ready/busy lines up aswell to points that arnt shown? I was hoping I could just solder all the legs to the matching ones on the original bios 1:1 (except for pin 12 for switching), but would this not work?

Thanks in advance 

[Tiido Priimägi]

Only having !CE lines lifted on both chips would do... chip that has the !CE used will be active, other not. also, you should add pullup resistors on both chip's !CE signals, so one could not be active while it shouldn't.

[Link83]

Only having !CE lines lifted on both chips would do... chip that has the !CE used will be active, other not. also, you should add pullup resistors on both chip's !CE signals, so one could not be active while it shouldn't.

Thanks for your reply, I think there is only one CE line on both the original bios and my replacement - which is pin 12. Could I connect them up like in this picture with a switch between the two?:-
http://cadcdev.sourceforge.net/hdwrprj/navi/gfx/04flash2.jpg

I am not sure what pullup resistors are? I havent really heard of that term before. Are pullup resistors just normal resistors and if so what value should I use? Do I just connect them in series between pin 12 and the switch?

[l_oliveira]

Pull-up resistors are used on inputs and open collector outputs to keep the logic level 1 on them while they are disconnected or not active.
In the case of inputs, pull-ups keep the input level at 1 while having high resistance, not causing trouble when a stronger signal drives a low level on the line. The best example of that are the inputs for the buttons on old style game pads.

So you put an pull up on the /CE (Chip Enable) lines of each one of the memories you want to select and a 3 position switch makes sure only one of them are enabled at a given time.

[Link83]

Thanks for your reply, so is Pin 12 usually ground? In which case would this switch work? and are 10k resistsors the right sort of value?:-

Thanks again 

[Tiido Priimägi]

in such setup you are not in a need for a resistor... and the original solder pad is not GND, but the signal to select the chip when needed. Having GND would result in bus fights as chip is always enabled and that's nothing good
You'd need pull up resistors only when you are going to use single section of the switch (outer ones go to chips, middle one is the enable signal from board).

[l_oliveira]

That's the suggestion I gave him through PM, man.  I find the 1 pole switch circuit safer because with pull-ups you have absolutely no chance of bus conflicts even in case of mechanical failure in the switch.

An even safer idea would be use a chip such 74lv138 or 139 to switch the /CE for the roms, allowing you to have an signal which doesn't come straight from an not replaceable component (the 315-6201 VLSI)