Tutorial written by : Arakon
Last edited: August 30, 2003

This modification will allow users of the older style PC-Bioxx to switch between 2 512 kb banks. I did this because I am using the xbox with the bioxx mostly for Linux experimenting, but wanted to play halo on it occassionally too. now I can switch between cromwell and an x2 bios.

This mod is NOT for beginners.. it requires precision and good tools. If you fuck your chip up, that's your problem, not mine.

"up/top" is where the parallel port connector is.
Locate the A18 pin of the flashrom (bottom left in the pic, the leftmost trace before the gap in traces).

CAREFULLY scratch off the green coating (I used a needle), about 1-2 mm long, before the trace runs towards the side. you can basically scratch anywhere, I just found this to be a good place.

clean the dust of the coating off, then apply a little solder to the copper so you can solder to it. now cut the trace behind the part you scratched, (NOT between scratched part and flashrom pin!). Solder a wire to the area you scratched.

solder a wire each to the top of the 2 capacitors as shown in the first pics.

Now solder the wire from the trace to the middle pin of a SPDT switch (2 positions, 3 pins), and the wires from the capacitors to the other 2 pins.

tape or glue down the wires carefully after testing.

click image for full view

Flashing instructions:

the bioxx flasher software won't recognize the switchability, so you have to manually flash the 2 parts. erase will work regardless of position.

now make/take a 1 MB version of the 2 bioses you want to use.

erase the bioxx, then load the first bios and flash.
it should give an error at around 0x08000 (if it doesn't, don't worry).
now flip the switch, load the second bios, and flash (without erasing again).

after that, turn off the box and try both switch positions. it SHOULD give you a different bios in each position. if not, erase and try flashing in the opposite switch position order (i.e. if you tried switch up, then down and it fails, try down, then up).