I've been trying to find out for some time exact EEPROM the Sega CDX uses (stock) which the bios is encoded on. The hope is that one day people will be able to source a replacement footprint EEPROM to load the multi-BIOS onto, instead of doing a mess of wires to a DIP package.
well the wait is over!
While working on a repair recently I noticed that this CDX was different from every other revision I've opened up so far...
https://www.flickr.com/photos/158377344@N04/32169518987/in/dateposted-public/
The EEPROM had a special serial number sticker attached to it. When removed it reveals...
https://www.flickr.com/photos/158377344@N04/40146822973/in/dateposted-public/
An off-the-shelf 1MB single programmable EEPROM! A Toshiba TC54H1024AF-10. Datasheet attached.
EDIT: I finally found the datasheet! Damn, that was hard. (attached). Courtesy of Datasheetarchive.com https://www.datasheetarchive.com/pdf/download.php?id=3c214888c0b962612a80392a2d0e20c0db0a75&type=O&term=TC54H