Over the holidays I had once again the pleasure of tinkering with my friend’s Amiga 500. This time helped him with flashing the HxC firmware to his Gotek floppy drive emulator which he had mounted in an external drive case. The flashing went smoothly, but in order to be able to boot from the Gotek device the Amiga needed a hardware modification.
This came as no surprise as we had done our homework. There are multiple products in the market but I did not really like them as they connected the IC pins to a DPDT switch with a long wire in order to swap the signals in pins 13 and 14. The CIA ICs are getting rare, and although unlikely, killing one with ESD would ruin the day. Moreover, the required switch type greatly limits the selection of switches and mounting methods one can use to make the solution as neat as possible. The prices of the existing solutions are also quite high if you consider the shipping costs as well.
For those reasons I created my own design. It is a really simple solution which uses a 74HC153 multiplexer to do the switching. The top side of the board has a precision DIP socket for the even CIA. The bottom part has the turned male pins for plugging the whole thing to the original IC socket. The circuit will draw its power (approx. 2 mA) from voltage supply of the CIA chip.
You can build your own Amiga Boot Selector by using these Gerber files: amiga_df0_df1.zip