Dreamcast mod chip/modchip program

[LeGIt]

Ola chaps

I'm just wondering if anyone has a sense on what the Dreamcast mod chip program does?

I'm assuming it checks for a code/frequency from point A (motherboard diode D501?) and transplants it onto point B (BIOS?) or vice versa, but does anyone know or have the mod chip program to hand or know specifically what it is inputting/checking/outputting and if so, when and where?

I have found the datasheet for one of the popular 4 wire IC's but as they are programmable they are not much use naked.

I ask because I'm not looking to flash the program as-is to a blank chip but I want to work out exactly what it is doing in the hope the region codes which are intercepted could be used for a region LED colour mod (orange for NTSC blue for PAL, or whatever you want).

I'm now one of the handful of people who own a Japanse, USA and PAL console so in theory if I had the equipment I could probe and find out myself - except I don't have the quipment - so I'm hoping someone more able/capable could furnish me with information or with the help of tools and region changer could join me on my journey of rediscovery.

I've forgotten most of what spent 5 years studying of electronics and this is my first real bash at it in 11 years so don't expect miracles from me - I'll get there in the end but it will just take me longer to complete the project.

Anyhow to summarise: If anyone has the Dreamcast mod chip/modchip program, it's source code or the specific region codes and details of it's programming such as a better understanding of what happens between the Dreamcast motherboard D501 diode, CE502 capacitor (just power?) and the IC501 BIOS ROM pin 28 and could share said understanding with me I would appreciate it.

[l_oliveira]

This is the change done to the MPR 21931 ROM chip to make it region free.


The multi wires chip do this change to the ROM every time it's read:
ADDRESS--DDDDDDDD-DDDDDDDD
------------76543210-76543210
0x00051e 00011110 10110000 (1EB0) <-original
0x00051e 00001000 10100000 (08A0) <-patched

I can't tell you how the four wires mod work but supposedly it patches more code, but instead it goes by changing one byte in several places to achieve the same result, probably around the same area of the ROM. Honestly ? Flashing is preferable because it's a much simpler solution, which as a side effect gives you a lot of room for customization (like for example the devkit logo on retail which is pretty slick.) :thumbsup:

[derekb]

This is the change done to the MPR 21931 ROM chip to make it region free.


The multi wires chip do this change to the ROM every time it's read:
ADDRESS--DDDDDDDD-DDDDDDDD
------------76543210-76543210
0x00051e 00011110 10110000 (1EB0) <-original
0x00051e 00001000 10100000 (08A0) <-patched

I can't tell you how the four wires mod work but supposedly it patches more code, but instead it goes by changing one byte in several places to achieve the same result, probably around the same area of the ROM. Honestly ? Flashing is preferable because it's a much simpler solution, which as a side effect gives you a lot of room for customization (like for example the devkit logo on retail which is pretty slick.) :thumbsup:

doesnt flashing involve wiring a whole new chips in place of your original bios chip?

[-=FamilyGuy=-]

doesnt flashing involve wiring a whole new chips in place of your original bios chip?

Yes, a small lot of people already did that. Works pretty well, region free and devkit intro.

[LeGIt]

hehe chers for the info - though I have a flash bios dc in the mail to me from APE :)

My goal is to recreate the modchip program in a PIC, but with an extra pin or two with small program to change the colour of an RGB LED depending upon the disc region, but in order to do that I ned to know how it reads and corrects the region ;)

Regionf re bios is cool of course, but region free dreamcast with orange for ntsc and blue for pal LED would be cooler still :D

[-=FamilyGuy=-]

My goal is to recreate the modchip program in a PIC, but with an extra pin or two with small program to change the colour of an RGB LED depending upon the disc region

I don't think the modchip detect the region and change the region flag in the FLASH accordingly. I **believe** it simply patches the bios to a region-free one. On a design side it's way easier to do.

You might have to put a *chip* on the gd-rom board to intercept the region read from the inserted disc.

[MrSporty]

You wont manage it in a PIC, it doesn't run fast enough to do realtime bios/dataline patching.

You could use an SX28, infact im sure one was used back in the day for this exact purpose.

[LeGIt]

Just checkd Farnell and the SX28 looks like a sexy beast, is reasonably affordable and in stock (albeit not so many). The Fluffy2 programmer looks like fun to make too though I can't do my own etching any more :( I think I have a friend who can etc but he is hard to get hold of betwen his missus and work... but he does have a decent oscilloscope too... hmm :D