Genesis ROM / Radica / Cartridge Slot Talk
Moderator:Moderators
- benheck
- Site Admin
- Posts:1880
- Joined:Wed Dec 31, 1969 6:00 pm
- Location:Wisconsin - Land of Beer and Cheese and Beer
- Contact:
Alright I have now found the pinouts for a Sega cartridge ROM. I checked Vectorman and Earthworm Jim 2, both late (1995) Genesis titles.
(Keep in mind my knowledge on CPU memory addressing is very rudimentary)
Let's start with the Genesis rom. Pictured is Earthworm Jim 2:
Ok, everyone remember all those 64k RAM 6502 CPU based computers like the Atari 800, Apple II, C64? The CPU had 16 address lines which allowed it to access 64k of data.
Every bit (lead) of address line you add DOUBLES the amount of accessible memory. In the above photo we see that EWJ 2 uses 21 address lines which makes it a 2 meg cartridge. Here's the math, watch how it doubles:
16 lines=64k (like an old Apple II)
17 lines=128k
18 lines=258k
19 lines=512k
20 lines=1024k
21 lines=2048k
The cartridge slot has 23 address lines so it could access.... that's right 8 megs! (or so I think...) As far as I know the 68000 CPU also has 23 address lines, so that's the max the Genesis can access (as opposed to some systems such as the Atari 2600 which had more access lines on the CPU than the cartridge slot, thus limiting its cartridge size to 4k rather than 8k)
Ok, now here's a pinout of the ROM. This matches both Vectorman and EWJ 2 (about the only two newer Genesis games I didn't mind ripping apart)
It has 42 pins total and 21 address lines, meaning this is a 2 meg rom. If the ROM is only 1 meg it omits an address line.
So here's what we know:
1) A Genesis ROM needs only 42 pins to be a 2 meg cartridge
2) A Radica ROM has 44 pins.
2 more pins... why, that makes 23! So, IN THEORY the Radica could have the same memory access as a Genesis.
The next step is a little tricker... mapping the lines on a Radica ROM spot. Once this is done, however, hooking it to cartridge connector should be a snap.
Let's WHUP this thing, guys!
(Keep in mind my knowledge on CPU memory addressing is very rudimentary)
Let's start with the Genesis rom. Pictured is Earthworm Jim 2:
Ok, everyone remember all those 64k RAM 6502 CPU based computers like the Atari 800, Apple II, C64? The CPU had 16 address lines which allowed it to access 64k of data.
Every bit (lead) of address line you add DOUBLES the amount of accessible memory. In the above photo we see that EWJ 2 uses 21 address lines which makes it a 2 meg cartridge. Here's the math, watch how it doubles:
16 lines=64k (like an old Apple II)
17 lines=128k
18 lines=258k
19 lines=512k
20 lines=1024k
21 lines=2048k
The cartridge slot has 23 address lines so it could access.... that's right 8 megs! (or so I think...) As far as I know the 68000 CPU also has 23 address lines, so that's the max the Genesis can access (as opposed to some systems such as the Atari 2600 which had more access lines on the CPU than the cartridge slot, thus limiting its cartridge size to 4k rather than 8k)
Ok, now here's a pinout of the ROM. This matches both Vectorman and EWJ 2 (about the only two newer Genesis games I didn't mind ripping apart)
It has 42 pins total and 21 address lines, meaning this is a 2 meg rom. If the ROM is only 1 meg it omits an address line.
So here's what we know:
1) A Genesis ROM needs only 42 pins to be a 2 meg cartridge
2) A Radica ROM has 44 pins.
2 more pins... why, that makes 23! So, IN THEORY the Radica could have the same memory access as a Genesis.
The next step is a little tricker... mapping the lines on a Radica ROM spot. Once this is done, however, hooking it to cartridge connector should be a snap.
Let's WHUP this thing, guys!
- benheck
- Site Admin
- Posts:1880
- Joined:Wed Dec 31, 1969 6:00 pm
- Location:Wisconsin - Land of Beer and Cheese and Beer
- Contact:
Oh, one questions: What's the best way to remove that white silk-screening from the Radica board without wrecking the traces beneath?
One more note: There's a good deal of components on the Radica board (even more than the NOAC) so I can totally buy it's an actual Genesis. The Genesis was what, a 68000, a Z80 and some RAM?
One more note: There's a good deal of components on the Radica board (even more than the NOAC) so I can totally buy it's an actual Genesis. The Genesis was what, a 68000, a Z80 and some RAM?
-
- Sir Posts-alot
- Posts:4186
- Joined:Fri Jun 04, 2004 4:10 pm
- benheck
- Site Admin
- Posts:1880
- Joined:Wed Dec 31, 1969 6:00 pm
- Location:Wisconsin - Land of Beer and Cheese and Beer
- Contact:
I've now checked about 7 different Sega carts (some have normal screws holding them together) and the pinouts and 42 pin ROMs are consistant. On average they have enough address lines going to the cart slot for 2 meg games.
I believe Streets of Rage 3 is 3 megs. Does anyone have that game to rip apart and check the ROM type?
-Ben
I believe Streets of Rage 3 is 3 megs. Does anyone have that game to rip apart and check the ROM type?
-Ben
- MM007
- Moderator
- Posts:1175
- Joined:Mon Apr 05, 2004 6:01 pm
- Location:In the wilds of suburbia...
- Contact:
To figure out the pins, try this:
Use a 512 K rom on the Radica and also use the equivalent cart in a normal sega(like Sonic 1 on both).
make sure they are doing the exact same thing(start up screen, paused at the starting pt. of the level, etc), and check the voltages on the cart slot. if you compare enough, you can start to eliminate things and find some of the pins out. ^^
Use a 512 K rom on the Radica and also use the equivalent cart in a normal sega(like Sonic 1 on both).
make sure they are doing the exact same thing(start up screen, paused at the starting pt. of the level, etc), and check the voltages on the cart slot. if you compare enough, you can start to eliminate things and find some of the pins out. ^^
Warranty-Voiding fun!
- SpongeBuell
- Senior Member
- Posts:5190
- Joined:Wed Apr 07, 2004 10:52 am
- Location:Colorado
- Contact:
-
- Sir Posts-alot
- Posts:4186
- Joined:Fri Jun 04, 2004 4:10 pm
Well this proofs once again that Ben supasses us all in knowlege about videogame consoles and portablizing them. As I've ripped my sega genesis apart I can use the cart connector to make my own once I find out how its done.
Again, great to here that you've made it work Ben
Again, great to here that you've made it work Ben
vskid wrote:Nerd = likes school, does all their homework, dies if they don't get 100% on every assignment
Geek = likes technology, dies if the power goes out and his UPS dies too
I am a geek.
-
- Posts:831
- Joined:Wed Dec 08, 2004 5:16 am
- Location:Chicago, USA
I honestly think it'd be safer to work the other way (putting the ROM into a Genesis cart using what we already know and seeing if we can't get it to work properly). We're also assuming something dangerous here- and that is that the ROM is simply a ROM. They could've encased something else into that part as well, and that is why extra pins are there. Though we also know that this is a 4MB ROM, because it says so right on it, so that means 22 address lines. So, in actuality, that is pretty unlikely. I'd say that a lot of trial and error is gonna need to happen unless someone can figure out a way to get at the epoxy blob and figure out which pins are going in which side of it, etc.
BTW, Sparkfist, he hasn't gotten anything to work, from what he's said...
Someone who has the Genesis Super SF2 should rip that apart and see how the pins are connected, since it's the only 40Mbit(48?) game I can think of. I'm sure you'd probably find that Ben is correct on that- it makes sense.
BTW, Sparkfist, he hasn't gotten anything to work, from what he's said...
Someone who has the Genesis Super SF2 should rip that apart and see how the pins are connected, since it's the only 40Mbit(48?) game I can think of. I'm sure you'd probably find that Ben is correct on that- it makes sense.
-
- Sir Posts-alot
- Posts:4186
- Joined:Fri Jun 04, 2004 4:10 pm