I haven't found any documents clarifying the drive select pins role with 3.5" drives. I have to disassemble a drive and see how the pins are routed on the daisy chain board.
That would be interesting to see.
Looking at the Mac Plus schematics, it looks like pin 16 is head select and its controlled by the 6522 VIA. Besides the change in what chip is controlling it, it should use the same logic across both machines.
It's labeled HDSEL on some diagrams, but on the Mac it's just a generic output pin (input to the floppy drive), used in combination with the other pins to read/write one of the 16 internal drive registers. That's the part that Floppy Emu needs the CPLD for.
If the pin goes high, the Apple 3.5" drive responds to the machine, if its low it ignores it since the instructions are bound for 5.25" drives. What makes matters confusing is how does the Apple 3.5" drive work on a Mac if this pin is grounded and unused?
Exactly. My proposed pulldown solution would work, I think, but it feels too weird to be the right solution.
let me know if and what you want me to test on the IIgs
I tried hacking pin 4 off one of my Floppy Emus, but the spacing is too tight and I couldn't find any good way to do it without damaging stuff. If you have one of those extension cables from IEC, you could try cutting the wire for pin 4, and see how that affects Floppy Emu with the IIgs.
