As I have the 1541 Ultimate II cartridge and not all software accepts to be loaded from device other than number 8, I decided to create a device number switch.
So I started to look around on the internet and found a nice solution on a Dutch forum.
It doesn’t only let you switch between device number, it also let you hide the drive from the computer.
It only needed a 3 pole 4 position switch.
But as I want my SX-64 to be returned in factory state, I also added some connectors and chip sockets to avoid cutting wires.
How it works…
On one of the VIA’s there are to pins, both pulled low by a connection to the GND line.
Cutting a trace on the circuit board (pads near connector P22) of one (or both) of the pins would change the device number (at reset).
I lifted the VIA and inserted a Chip socket with wires attachted to the pins 1 (GND), 15 (PB6?) and 16 (PB7).
the other side of the wires, I mounted on the switch.
Now the address of the drive can be selected.
Now to hide the device from the serial bus I disconnected the internal serial cable to the floppy drive board and created a little connector extension that feeds all signals 1:1 through.
So now when the switch is in the first position the device will act as drive 8 (ATN connected and both VIA pins to ground).
In the second position it will act like drive 9 (ATN connected and only pin 16 of the VIA grounded), in the third position the drive will act as drive 10 (ATN connected and only pin 15 grounded).
In the fourth position the drive is hidden from the bus as the ATN line is disconnected.
As the drive does not get a ATN (Attention) signal, it will not react on any request on the bus.
To nicely mount the switch without drilling a hole in the case, I moved the fuse holder inside of the case and used the hole for the fuse for the select switch.
For this I disconnected the fuse holder, and reconnected it on the inside.