This is my first attempt at designing a flash cartridge for the ATARI 5200. The cartridge employs the ATMEL AT29C256 flash device. I also have a design for a simple parallel port flash programmer for this device. The ATMEL flash devices can be ordered from Arrow Electronics for around $5 each.
Schematic capture and layout were accomplished using EAGLE Light from CadSoft. Considering that it is free (as in beer), it is a decent tool.
The 5200 cartridge interface is designed to accomodate one or two banks of ROM, each bank being either 8k or 16k in size. Because of this there are only 14 address lines plus two bank select lines. To accomodate the 32k flash, the upper and lower bank select lines Y1 and Y2 are used to generate the highest bit of the 15-bit address as well as the output enable (OE) input to the flash device as follows:
OE = Y1 * Y2
A14 = Y1
Layout was also accomplished with EAGLE Light. Here is the .brd file.
The original prototype was created from a modified SEGA Star-Trek cartridge. PCB prototypes were created by PCB Pool. I'm very pleased with their prices and results. I highly recommend this manufacturer.
I apologize for the poor quality of these photos. I hope to replace them soon.