Have you ever wanted to use a Gotek on your Amiga without having to make changes to the Amiga itself? I think too many Amigas are being “mutilated” to fit a Gotek these days. Instead you could use the internals of an external floppy, and change out the floppy with the Gotek. problem is, many games require to boot from DF0: This is where this selector is being handy. Models with SMD CIA, like A600 and A1200 can not use this device. Since they have internal HDD interface, they can just use WHDload games instead.
Background: The CIA chip (Complex Interface Adapter) inside the Amiga is used for communication like the Serial Port and the Parallel Port. But thats not all it does.
The Amiga Computer uses the CIA chip to determine the floppy drive ID (DF0: or DF1:) This is done by pulling select lines low. There are several select lines, D0, D1, D2, D3. If you for instance swap pin 13 and pin 14 on the chip marked Even CIA (U8) on the Amiga 500, you will make DF1: to be DF0: and vice versa. Normally, the internal drive is DF0: and any external drives is DF1:, DF2: and so on. But what if we want the external drive to be DF0:? That can be done by simply swapping pin 13 and pin 14 on the CIA chip. This is where this switcher comes in. I browsed the net for ready made solutions, but the ones I found, was mostly 2 sockets soldered together and a switch and usually sold out, so I decided to make my own switcher, but with a real PCB. This design uses a HC153 multiplexer instead of just a normal switch to swap the pins. I would hate to damage my CIA with just a manual switch. With this selector, the CIA is a lot safer.
I decided to make one with normal dual wipe socket and normal pins, (right) and one with “turned pins” (round pins) The idea is to remove the CIA from its socket, and put this there instead of the chip, and then put the CIA in this socket. You can use this by simply leaving a jumper in or out. One can easily use a switch where the jumper resides to change the setting without opening the computer. Personally, I wont be changing the switch often, so Ill go with a jumper, since I dont want to make a hole for the switch. These days I mostly start my software from a Gotek, so I dont need the internal drive for other than copying disks. Since many games require boot from DF0:, its good to be able to boot from an external Gotek and make it DF0: Now I can leave my Amiga intact instead of hacking it up to install a Gotek internally. With this, the internal disk is now DF1: and the Gotek is DF0:
You can use this image to identify where to put the parts. The cap is hidden under the socket in the left, and the 330 resistor (marked 331) goes to the left, and the 10k resistor (marked 103) goes to the right in this image.
I sent my gerber files to a PCB factory, and they works great!
This project with PCB and parts can be purchased on ebay: https://www.ebay.com/usr/kirsti_73
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