Sega Megadrive Address Checker: Formerly "Unknown PCB"

Has anyone any idea what this pcb could be? I guess a CPU test board. Can that be right? For which system could it be?

 

I'll take a guess that it's for testing and arcade board as opposed to a console.
Might be completely wrong though.

The CPU looks like a Hitachi HD68HC000P12, which is a CMOS version of the 68000 used in the MD/Genesis.

 

Would it connect to the side slot on a first model mega drive? connector looks to be about the right length.

 

If ASSEMbler is right about the Mega-Drive relation it's probably the only place it would fit on an MD. Give it a go and if it goes all boom-shaka-laka on you, then you'll know it wasn't a Mega Drive tester.

 

That was the one cart out of the lot that caught my eye. Probably should've just bought it.

Nice to see a higher res image of it, anyway. Piece of history right there.

 

It's an address checker... It checks whether game samples access restricted memory (undecoded or mirror addresses); important for upwards compatibility.

 

It must be a addresschecker. There ist an adapter which connects this pcb with a 66 pin ic-sockect. I think i have do desolder the cpu of a genesis v1 and replace it with this adapter.

 

I used to have a megacd with a port like this on the back, so possibly megadrive with port like this exist too.

 

No, i think that the mega cd dev port is to small. It looks like 16 pins per row. This one has 32 pins per row.

I added a picture of the adapter. The adapter would fit perfectly on a mega drive 1 board with unsoldered HD68HC000P.

 

Yeah, but it may well have been intended for a dev unit. If you try it, be sure that you get the adapter the right way round!

I missed this auction, sadly! Well done on getting it! Does anyone have a link to the auction? What else was being sold?

 

Empty Megadrive proto cart PCBs as I recall.

 

Oh, those I saw! Didn't notice this among them, though! :\

 

Is it that interesting? It's really not useful outside of Sega or very difficult to make your own. Probably no retail software will even trip it. And yes it just drops into the place of a 68000. I'd put it in another socket to not devalue it.

 

Cool item. I see all kind of switches on the board too.
Any idea what kind of information the led display will give?

Make sure you make a video when powering up the megadrive with this pcb for the first time, it will be exciting to watch. ;-)

 

:/ Being an address checker it will show an address on the 7-segments... 6 hexadecimal digits = 24-bit address.

It monitors the address bus for accesses to hardwired illegal memory ranges, and when they occur it will halt the CPU. From there the operator can see the program counter (address of the offending instruction), the illegal memory address, whether it was a read or write, whether it was a byte or word access, and presumably the data at that address.

The point is to track down bugs which would break compatibility with future hardware and upgrades. Since retail games will have already gone through this to be licensed to play with the thing you'd probably have to homebrew a test.

 

Ok looks like a sega mega cd dev iteam plus i wonder if it would work.