Description
This cartridge allows access to the 3.5MB of additional ROM space of the Commander X16 offers via banking. It also allows up to 512KB of EEPROM storage using four Onsemi CAT24M01 I²C EEPROMs, each supporting over a million writes and rated for 100 years of data retention—ideal for save-state data and other persistent storage.
The cartridge ships completely assembled with one blank 512KB SST39SF040 nor flash IC. You may add up to 6 more 512KB flash ICs via the drop-down if you would like more space. Additionally, up to four I²C EEPROMs may be added. Each adds 128KB of persistent storage for a maximum of 512KB. These chips are optional, and only needed if save states, or data storage is required.
Technical Overview
The Commander X16 supports up to 4MB of ROM, with 512KB already onboard. The cartridge accesses the remaining 3.5MB via the expansion bus using up to seven Microchip SST39SF040 512KB NOR flash chips. Smaller chips like SST39SF010 (128KB) or SST39SF020 (256KB) may be used, they will wrap within their allocated space (e.g., a 128KB ROM repeats four times in a 512KB region). Using smaller chips may reduce cost for cartridges which need less space in the final ROM position.
We do not offer other chips at this time. It is also important to mention that the TSOP form factor of the SST39SF040 is now dicontinued. We do have a large number of these chips available. Inevitably we will run out and need to redesign this board. Getting TSOP 128KB and 256KB versions of the chips may be difficult now. The redesign will not change functionality, just the form factor of the NOR flash chips themselves.
Features
- Write Protection: Cut JP1 to write protect U1-U6, JP2 write protects U7
- Writing to EEPROM: Requires KERNAL I²C routines, with each chip appearing as two addresses (e.g., $50 and $51 for 64KB each). Addresses $52-$57 cover the remaining chips. EEPROM read/write speeds are slower but suitable for persistent data storage.
- Ongoing Development: Example code for EEPROM interaction will be released as development continues.
For more details on EEPROM interfacing, refer to the CAT24M01 datasheet, and for Commander X16 I²C routines, check the X16 KERNAL documentation. The SST flash ICs may be programmed with the excellent utility written by FlightControl: the CX16 Update program. This program was primarily written as a utility to update the SMC, VERA and system ROM, but it is also handy for updating the ROM within the cartridge space.
Cartridge Shell Notes
We have only been able to source two colors of cart shell which fit our PCB design. More were available when the board was initially designed, but they seem to be unavailable now. Mild PCB filing around the notches may be required to get the boards to fit in some shells. We should have made the notches wider, as more variations in the cases are present now than when we tested initially. That aside, they will fit without too much fuss. Please note the hole on the left side of the front of these cartridges. If you are looking for other options on the internet, be sure they have this hole in the upper-left hand corner. There are about 3 or 4 different styles of cartridge shells for the Famicom out there. We used these as they were the most robust and a bit larger.
Whoops
There is a minor mistake with the board. The NOR flash chips need to be populated in reverse order. I mislabeled the decoding in the schematic, which led to this mistake. I was going to rerun these boards, however, that is when I realized the TSOP chips were no longer available as well. So not wanting to wait longer for a cartridge to release, we’re just putting these out until we run out of chips. Just remember they are just mirrored. IE, U1 is really U7, and so-on. The board pictured is with one chip in the reverse (correct) position for a 512KB board.
Be sure to see the listings for 3.5MB ROM Board, if you would perfer that form factor instead. They are functionally equivalent, but the ROM board may be a little more user friendly for cartridge development.
