SEGA Mega CD Multi-Bios / Which Switchless Code?

Hello All.

I am starting my Mega CD Multi Bios research to hopefully do the mod next week.

I have a few simple questions.

All the online examples are using Seb's code for the Mega Drive switchless mod, can this be achieved with D4S code as I would prefer to use that? If so which two pins of the PIC16F630 need piping to the Mega CD port pins?

These are pins 8 and 10 when using Seb's code. As far as I can tell these are not used. I can not find the information to tell me what these pins actually do or if they correspond to anything on D4S code.

Is there a pin out diagram for Seb's code that does not label pins 8 and 10 as free?

(Image https://circuit-board.de/forum/index.php/Thread/15341-Sega-Mega-Drive-1-Switchless-Mod/)​

Many thanks

 

Why not use the region-free Japanese BIOS instead. The only problem I can see with that, is that the save game manager is in Japanese, but I haven't found that to be a huge problem as the icons explain this pretty well

 

Really like the idea of having an all in one Mega CD that can display all the different regions BIOS.

If it can't be done with D4S I will just have to use Seb's code which all the guides are for, it's a pretty simple mod but was hoping I could use D4S.

 

I haven't done this mod but if you mean having all BIOSes on one EPROM like described at http://wolfsoft.de/wordpress/?p=407 then it appears that Pin 8 is inverted region select and Pin 10 is inverted language select. I'm not sure if this is a modified version of seb's code or if seb's original does this but if d4s or borti's don't have this you could use an inverter chip or just change the EPROM layout. So instead of the order used by wolfsoft, usa.bin + pal.bin + jpn.bin, you could either pad the beginning or use any bios and order it, (any bios) + jpn.bin + pal.bin + usa.bin. Then you would connect PIC Pin 9(d4s) to EPROM 38 and PIC PIN 10(d4s) to EPROM 39.

Side note if you are doing a region free Mega Drive, there is another option with in game reset built-in https://github.com/SukkoPera/MegaDrivePlusPlus/wiki

* edited to correct pinout

 

Thanks for this.

Yes all bioses on one chip.

I believe this should be standard Seb code since neither wolfsoft or mmmonkey mention any modification. And those pins are used in the Saturn mod, but I am new to this so I could be wrong.

I will give your inverted bios order a try. I now have that luxury after taking possession of a Mini Pro and 27C adapter.

Will look into inverter chips too.

MegaDrivepPlusPlus is on the list for another MD I own.

Thanks loads

 

Hello.

This is my progress so far.

1. I downloaded the three No-Intro Mega CD BIOS files.

[BIOS] Mega-CD (Europe) (v1.00).bin
[BIOS] Mega-CD (Japan) (v1.00P).bin
[BIOS] Sega CD (USA) (v1.10).bin

2. Renamed them as eu.bin, jpn.bin, usa.bin for convenience.

3. byte-swapped these individually with GadgetUK164's byte-swap program.

4. I then combined them, including an extra at the start, into a single file with CMD 'copy /B extraeu.bin + eu.bin + jpn.bin + usa.bin d4s-multibios.bin'

The resulting file is exactly 512k and everything looks present.

Next step to take.

5. Burning the MultiBIOS

I have a bunch of AT27C4096-90PU chips but they are not the erasable type and they cost about £6 each. Not cool. So I really don't want to mess this part up.

I would like confirmation on the order of BIOS files. I have done a little research and tried to document it as logically as possible, but I am a complete newb to this so it would be great if someone can have a quick look and tell me if I have misunderstood anything.

Have to upload an image as I am not sure how to make tables here.



So holding reset on the MD would cycle through Bank 2, Bank 4, Bank 3, repeat.

Is this ready to burn?

Many thanks for all your help.

 

I looked into this further and like you said mmmonkey's guide(http://www.mmmonkey.co.uk/sega-saturn-switchless-region-and-video-mod/) for region free Saturn uses the other pins and the truth tables matched the tables listed by wolfsoft. I then looked at seb's guide(https://knzl.at/saturnmod/) and found that the tables did NOT match those found on mmmonkey and wolfsoft's guides. Mmmonkey's guide uses the correct mapping from PIC to the Saturn but the truth tables are not correct. So that means Pin 8(seb) is inverted region select and Pin 10(seb) is inverted language select. So yes if you use Pin 10(d4s) to EPROM 38 and PIN 9(d4s) to EPROM 39 then the order you listed will work. I have corrected my previous post so as not to confuse anyone else.

 

That's great thanks. Gonna burn a chip and try do the install on Thursday. Will post my outcome and video, etc., when done.
Thanks loads.

 

Hey you contacted me on Youtube, here's a better answer.

As I told you, I'm going to simplify my switchless mod and get rid of the LS00.
I'm using D4S code.

It will depend on which pins LANG/VIDEO you are linking your eprom pins.

If you pull high-low logic on the EEPROM this will work like that:
0-0 access to the FIRST memory bank of the EEPROM (the lowest)
1-1 access the LAST one (the highest)

So the first one should be the original one in case you plug the console in an unmodded console, at least the default bios will be used (it will consider the pin as open)
the last one should be the USA.

The two others won't matter. Let say you burn your order: eu.bin + eu.bin + jpn.bin + usa.bin
Now If you boot your Megadrive in EU (Lang 1 video 0) and got a Japanese bios, you'll just have to swap the wires to your eprom.

For exemple, I have a Japanese MegaCD, and my order of burning is
jap(default) -> eu -> jap -> usa
because D4S code's order is: usa -> jap -> eu (so it's mirrored)

But I could also have:
jap(default) -> jap -> eu -> usa
because D4S code's order can also be read as: jap -> eu -> usa (same order)

Hope this will help you.

 

That's great help. Cheers

Yes I figured as much, wire order just determines the order of the middle two BIOSes.

Still not done it yet, as just did my 32X first. Just ironing out a few problems with it and will get onto the Mega CD. Pal unit seems to be stuck in 60Hz after the mod, yet is allowing out of region games to play. Think the link cable might be suspect.

[EDIT]

Confirmed that the RetroGamingCables stereo link cable does not contain the mono audio line. So I have to build a new cable with all three audio lines.

 

I finally progressed with this.

5. I burned the MultiBIOS with my TL866ii Plus onto a AT27C4096-90PU. This was quick and straight forward.

6. Installed into my Pal Mega CD which already had a socketed BIOS so I did not have to desolder the chip and add my own socket, even though I had prepared for doing just that. I bent up pins 38 and 39 before pushing the chip into the socket. Tinned the two pins and two pads and wired it up. I soldered the two wires into the bridge connector also. I made a massive mistake with this. Once the wires were on, the bridge connector case would no longer close. The circuitboard came with a large magnet that surrounds it and the wires prevents it from sitting flush. So I dremmeled the magnet down to make a tunnel for the wires. Unfortunately it was actually a plastic wall on the case that was preventing it from closing so I then dremmeled a small gap for the wires and everything closed up perfectly. Just wasted my time dremmeling a magnet but it was a neat job so nothing looks bad or lacks integrity.

7. Test. The default European BIOS loads up and the system is working. This is a great sign.

My next step is to add the extra wires in the Mega Drive to the connector to change BIOS with the Mega Drive reset. But it's looking good that everything should work.




Pointless Magnet dremmeling


The cut that was required.

Does anyone know how good the European Region free BIOS file is? Maybe I could burn that one as my default instead so the Mega CD is region free by default.

Cheers

 

Like 3 games dont work. All games work with the japanese bios

 

Ok cool. Cheers. Will try that next time.

 

Hello.

I finally finished the extra wiring in the MD to control the MultiBIOS and everything works.

I now have a switchless multi region Mega Drive / Mega CD / 32X tower of power.

Very happy with the final results.



I made a little stripboard for the switchless mod. Think this would be a nice little project to learn Eagle and PCB design, so that's my eventual plan.
32X Video Refresh Rate (Green Wire to Mono Audio Out)
Mega CD Region Select (White and Grey Wires)

Cheers

 

Hi.
I want to put the Japanese Region Free BIOS in a PAL Mega CD 1 unit as a single BIOS machine.

There are three Japanese MCD1 BIOS files in l_oliveir's BIOS pack v2.

Which one do I use?
jp_mcd1_911217_regfree.bin
jp_mcd1_911228_pal_regfree.bin
jp_mcd1_911228_regfree.bin

Many thanks

[EDIT]

Scratch that, I found the relevant thread.
Cheers

 

When you are charging as much as you do on ebay, you can figure it out.

 

It's a great way to fund my new hobby and buy new tools. Obviously eBay is fair game so I really don't see the problem. I priced everything lower than anyone else on eBay. I don't sell here or even advertise here because I would never impede. So there's literally nothing to twist your knickers about.

But FYI you shouldn't judge, because you don't know me or how I've been walked all over my entire life. For the first time ever I took some initiative and I am rolling with it, regardless of who it upsets. Others do it, so now I am too.

Cheers.

PS, I am literally sat in front of a Mega CD right now. Just removed the BIOS. Added a socket. Burned the new BIOS and am about to close up and test but have had to write this now. I charged £33 including return shipping. That's a pretty reasonable price considering eBay fees, PayPal fees, and return shipping.

Oh and that particular Mega CD BIOS is an AT27C4096 chip at the cost of £5+ and look at the quantity. I am selling three of them and buyers can choose to have a MultiBIOS. £5 + eBay fees + PayPal fees + padded envelope + large packet post delivery. I might make a couple of quid. I am a scoundrel aren't I???. I even do free mods for people and was also planning on having a week of £1 eBay mods. But I guess the narrative of the massive screen shot must prove I am a scheming rip-off merchant out to fleece you all with inflated prices.

So long Assemblergames. Was swell.
Thanks

 

Point is, you are charging for it. You should know what you are doing. Not posting on a forum for how to do it. Doing stuff for a hobby vs doing things commercially have different rules. If you sell a service, you should know what you are doing.

I don't care what you charge, else I'd be selling on ebay and clean up. I care you want to sell things you don't know how to do or don't know what to provide.

I wouldn't like to call a plumber, pay him and find him watching YouTube in my kitchen on how to fix the issue for example. But if my mate came round to help and did the same thing? No problem.

Helping someone modding their own stuff that wants to learn? Also no problems.

 

Also, I suspect screenshot is massive because mobile and my phone is high res screen, so the screenshot is massive.

 

I understand your concern. But you need to give me some credit. You don't need an electronics engineering degree to do a Mega Drive switchless install or to burn a chip, not even to replace the voltage regulator and do a recap. For the most part, these are manual jobs I've learned to do just as well as anyone else.

But I do have a BSc and an MSc in technology related subjects, not electronics but I'm no lightweight to understanding complex systems. This accounts for my fast development and why I feel I can now charge for doing a Mega Drive switchless install and why I learned Eagle in a day, from finding out what it was to having an order with OSHPark for my own Mega Drive switchless board that I will use in my installs.

I've devoted almost everything to this, time, energy and money. If I ask a question here, I probably devote the next month to understanding more about it. I sometimes need clarity or a second opinion like I did here with that Jpn-Pal BIOS which momentarily confused me.

I'm not selling a repair service or claiming to be one. Only very low quantity of easy to do mods that I go above and beyond with in such a niche market that I might get to do one every couple of weeks. If you don't believe me look at how I do the Mega Drive switchless LED install into the top case. It looks like SEGA did it. It took only two iterations to get to that stage. Not seen anyone else do it like that. A blob of hot glue will do from the professionals at the "retro" stores. I also pass all queries for repair or mods that I've never done onto other places and all my research and knowledge will be passed on as better install guides than currently available so others can do it themselves much easier than I could. And the cherry on the cake is, I get to undercut all the "retro" shops charging casuals £60 for a MD switchless. There are no losers here.

Anyway, we can move on from this and end this little detour. No harm, no foul and no hard feelings.

My Sega Tower of Power Switchless MultiBIOS mod.

Mega Drive Switchless (Soon with custom PCB)













My 32X Auto Hertz



My Mega CD MultiBIOS Swap