I'm making simple rewritable carts for a while.
But they were quite rudimentary.
Now I'm planning building a 2Mbytes cart for Genesis.
I'll use TSOP or SO flash memory chips, and original cart with SRAM, to replace ROM.
To build a cart from scratch, you need 2 side photosensitive PCB, TSOP chips (and tools and hability to solder these), SRAM chip and some decoders. It quite simple.
the problem is programming.
You would like to add some sockets in order to remove the flash ROM easily and program it in a PC programmer. For example (like Willem).
I'll programm it using a expansion port cart I've made, to boot a BIOS I'm writing, that provides me with flash routine functions (for onboard chips, in expansion port, or cartridge port), as well as computer comunication using a simple cable.
http://personal.telefonica.terra.es/web/co...re/bienveni.htm
In "proyectos" you can see these project.
It is Spanish, but that section is in English.
Using SD or CF card is a great idea, and I'm researching on it, but it is NOT easy as it seems. The memory timings are critical, and you would need *at least* to use some sort of DRAM (very hard to use due to refreshing requirements), or expensive SRAM as buffer, along with a complex logic circuit (CPLD or FPGA) to implement the protocols to interface the card.
