Modified Sega Megadrive - what did they do to it?

I have a Sega Megadrive, it came from a developer, and it seems to have had a brain transplant and several holes drilled into it (for switches?):











Any ideas what the modifications were for?

 

WHAT THE.... that cpu is socketed, what was he trying on that poor MD, opening and check if there are any soldering job or some joint that might been touched wold help to know what the... happened there

 

The socket allows an in-circuit emulator to be fitted. Other holes could be for anything.

 

You're confusing a useful purpose with "being really, really drunk".

 

I'll take her clothes off tonight and see if there's anything else different inside. I have two more with the same holes drilled into them, US models, but no gaping hole in the top. Perhaps they too have sockets fitted, I'll find out tonight.

 

looks more like someone had the idea of overclocking and adding region switches, then they started cutting the case and thought "FUCK IT" then just melted it with a soldering iron and used a screwdriver to try and break the case apart rather than use the screws provided lol

 

I bet with you that console had an ICE debugger installed in it and it was removed later and sold separately.

An ICE debugger is a piece of equipment that allows you to single step instructions, break execution anywhere, dump memory and read CPU registers in real time as a piece of code is executed on real hardware.


To make that possible, the ICE hardware has to sit between the machine hardware and the CPU chip. hence the case being cut that way. :thumbsup:

Edit: Ops I just noticed that Calpis had replied this already with the same answer, just different wording.

 

Well, nothing much different on the inside. I guess there's some pieces missing - what does an ICE debugger look like? Does anyone have a photo? Google isn't much help on this one.

 

Just look at the MEGA-CD/SEGA-CD devkit which has an sort of In Circuit Emulator (ICE) built in the MEGA-CD.

Also this is an ICE for Intel 80186/286, which is good to give you a idea what an 68000 ICE would look like:

http://www.testech-elect.com/nohau/emul-196.htm

 

Cheers, so it's pretty much useless without some extra bits

Here's another one, a US Genesis with the socket installed and a very flimsy switch:

 

If that switch goes to this jumper point on the PCB, then it is for region switching and possibly language switching too:

 

Looks like a rushed modification: who did that didn't cared at all about ruining the case

Cheers,
Oge

 

Yeah, it's been used with an ICE unit attached. See the following link for an idea how it would have looked with the ICE unit connected:
http://www.x-cult.org/cat/15/Genesis%20-%20Megadrive/94/ZAX_Megadrive_Dev/

 

The modded case in that picture looks exactly like mine. Does anyone have one of those ERX 318P boxes for sale? I'd be very interested in getting one of these up and running.

 

Well, Dano2k0 has the manuals for sale right now:
http://www.assemblergames.com/forums/showthread.php?37034-Very-rare-ZAX-ERX318-manuals

In terms of the hardware itself, they're quite rare units, very expensive back in the day. I've seen them come and go a few times over the years, though I don't know if I've ever seen a complete unit, meaning the ZAX unit and the PC cards and software to go with it. Assembler used to have the unit itself, in fact, I think he used to have that very one that's pictured on x-cult, but I believe he sold it a few years back ( http://www.assemblergames.com/forum...-dev-hardware-50-miscellaneous-items-for-sale ). I should note, that description of what this unit does in that link I posted before is a bit misleading. What the ZAX ICE unit allows you to do is simply do remote hardware debugging for the 68000 processor. The ICE unit replaces the 68000 chip, and acts in its place, while providing a host of debugging and monitoring functions to the developer. It doesn't, by itself, allow you to do anything special in terms of running code on the system, but the picture showing the ZAX unit in that link does have some kind of Mega Drive development cartridge sitting on top of it, and it's not one I recognise. It looks like it's loaded with volatile memory storage rather than SRAM or EEPROM chips, but I don't see any evidence of an interface port or anything on it to load data into it directly, so it does seem likely that the ZAX ICE unit would have been used to write data into this cartridge after booting the system. You would require a unit like the ZAX in order to make use of an entirely volatile cartridge like that. It would have been very fast to write to though.

Like most of these units, you need the complete ZAX kit, with the ICE unit, software, and interface cards, in order to make use of it. I don't think I've ever seen a picture of the interface cards that came with the ZAX 318P, which emulates the M68000, but Charles MacDonald managed to get his hands on a complete kit for the ZAX 308P, which is for the Z80. You can see a lot of info he posted about the ZAX 308P in this thread:
http://www.smspower.org/forums/viewtopic.php?t=12038

 

I should note, the SNASM2 ICE unit in the Cross Products MegaCD dev units performs the same kind of task as this ZAX system, though I'm not sure how the two compare to each other in terms of debugging features. The SNASM2 is quite small; they manage to fit two 68K ICE units onto that single bridge board in the Cross Products system, and a single small interface card communicates with the hardware, whereas the ZAX ICE is huge, and requires two massive ISA cards to communicate with the hardware. It's possible the ZAX is more powerful/has more features, but it's also possible it's simply older and not as clean a design. We'd need to see the ZAX 318P and SNASM2 manuals to be sure.

 

Oh, I should add one thing: Those other holes you see cut into the case are most likely for probe connections from the ZAX unit. From looking at the ZAX 308P unit Charles posted info on, I can see it had some hardware probe leads, which allowed some extra channels into its internal logic analyzer. It seems like the ZAX unit actively logs all bus signals, as well as some extra ones the user can hook into with those probes, and when a breakpoint is triggered, the developer can see the recent history of the bus through the logic analyser. Now that's something the SNASM2 can't do, that's for sure! Those probes were most likely connected to signals of interest, perhaps lines like VSYNC/HSYNC, or whatever else the developers felt like monitoring at the time that wasn't directly connected to the M68000.

 

Cheers for the info. I've made an offer for the docs (for the new docs preservation project, if anything) and I'll do my best to get hold of an actual kit.

 

Just adding a bit here: By what I've seen on pictures of the SNASM2 kit internals (MEGA-CD) it seems that the ICE device is installed on the 68000 CPU that belongs to the MEGA-CD unit and not on the MEGA DRIVE CPU, which makes a lot of sense as it's a kit meant for development of CD-ROM games.