Some notes:
First of all I realized I've made another DUMB mistake - when I relabeled the address lines on my drawing A0-A20 I forgot A0 when counting the lines! This means the Radica has 21 address lines allowing for 2 meg games (instead of my erroneous guess of 20). So the Radica can access 2 meg games. However I don't know why some older titles (like Afterburner or Ghouls and Ghosts) don't work, I highly doubt that are even 1 meg.
I should have realized this stupid mistake when games like EWJ2 and Batman & Robin (clearly not 1 meg games) were working.
So this DOES NOT invalidate the pinouts I posted, it just invalidates my ability to count
If anyone has ROMS of Genesis games that tells the size... so 2 meg titles like Contra Hard Corps will work but 3 meg Streets Of Rage 3 won't... in theory. Be a good way to test. (Will need actual carts as well)
Cartridge connectors:
Goto Digikey.com and search for "card edge connector" with 64 contacts. 3 choices will come up, they'll all work as far as I know (Can't quite remember which I ordered, but the pitch is important as it refers to the size/spacing of the contacts themselves)
40megaBITS is actually 5 megaBYTES. BYTES is BITS divided by 8. Megabytes are what our computers measure stuff in nowadays, BITS was a way (I've always assumed) of making the games sound bigger than they really were.
I was always a little confused by this until I started seeing the size of NES roms in emulators in the late 90's. 128k games (Contra, Zelda) were called 1 megaBIT games in the magazines. One 8-bit byte has 8 bits (obviously) so that's where it comes from. "128k" or "512k" are intangible terms, where MEGABIT sounds cool to a 13 year old.
The Genesis cartridge slot has 23 address lines so it should be able to access up to 8 megs. Unless it's somehow crippled to 4 and that's why an extra bank is needed to access 5 megs (Street Fighter)
But getting bogged down by these now-BS terms like "megabit" really hampers actual progress in figuring out cart sizes, how many pins you need, etc. So let the BITS rest in PIECES.
EVERY ROM contact from the Radica has been used... as compared to a regular Genesis ROM it has an extra VCC (+5 volts) and a pin (pin 1) that does nothing. The N/A contacts listed on my cartridge out aren't needed for most games, and if you take games apart you'll see no actual connections go to those spots (from the ROM) Crap like the 32X probably uses them for staying N sync.