PWM is only needed by 400k drives from what I read. The IIgs doesn't support them at all. Pin 10 may not be used by the IIgs despite having an assignment, I have used the A9M0106 800k drive on early 400k Macs without a problem despite the PWM signal being present. Its also possible that the write protect pin is used by the "smart" Unidisk 3.5" drive which can't be used on a Macintosh at all without risking stuff blowing up!
As for Drive 2 Select, the IIgs supports daisy chaining two 3.5" drives on its floppy port, something Macs can't do (there is no internal drive on the IIgs). The pass through board in the Apple 3.5" Disk (A9M0106) likely controls pin 9. It might not be required for the floppy emulator to work, but it might restrict the floppy port to just one drive.
Basically when the machine wants to access drive #2, it activates pin 9 instead of pin 17.
I still think the problem is with pin 4. Since the IIgs floppy port supports both drive types, it needs to be able to determine which type its talking to. The Apple IIgs Setup guide specifically states that all 5.25" drives must be connected after 3.5" drives on the chain. Its likely this pin is left floating on 3.5" drives, but I'll try and dig up more info on how it works. Uniserver could be daring and disconnect pin 4 from ground and see if it works.....
As for Drive 2 Select, the IIgs supports daisy chaining two 3.5" drives on its floppy port, something Macs can't do (there is no internal drive on the IIgs). The pass through board in the Apple 3.5" Disk (A9M0106) likely controls pin 9. It might not be required for the floppy emulator to work, but it might restrict the floppy port to just one drive.
Code:
"The UniDisk uses pin 9 to select the second drive. Inside each UniDisk, the signal from pin 9 at the computer is connected to pin 17 of the daisy- chain drive connector. When the computer selects drive 2 by activating pin 9, the first drive passes this through and the second drive sees its enable signal on pin 17. Thus all drives are identical."I still think the problem is with pin 4. Since the IIgs floppy port supports both drive types, it needs to be able to determine which type its talking to. The Apple IIgs Setup guide specifically states that all 5.25" drives must be connected after 3.5" drives on the chain. Its likely this pin is left floating on 3.5" drives, but I'll try and dig up more info on how it works. Uniserver could be daring and disconnect pin 4 from ground and see if it works.....
Code:
"Despite the IIgs having special functions for pins 4 and 16, they may be ignored when dealing with 5.25" drives, and treated as a UniDisk controller (i.e. connect pin 4 to ground, and pin 16 to +5V). The Apple 3.5 drive disconnects these signals internally, so that they will not interfere with its operation."