Just a thought in my head on possible daisy chain board logic.
At the IIgs disk port:
If pin 4 is grounded on the port, first drive is 5.25" thus no 3.5" drives detected
If pin 4 is not grounded on the port and there is a ground present on some random pin, first drive is 3.5", probe to see if there are two drives
3.5" drive in the chain:
If pin 4 is grounded on daisy chain port, drive is 5.25", route drive select 1 signal to pin 17, only activate if input pin 4 is low from computer.
If pin 4 is not grounded on daisy chain port and there is a ground present on some random pin, drive is 2nd 3.5", route drive select 2 signal from pin 9 to pin 17 (this is how the drive avoids receiving the damaging PWM signal on a compact Mac, it never makes it to the floppy drive to begin with!)
If pin 4 is not grounded and there is no ground present on some random pin, drive is last in chain
This configuration only supports 2x3.5" drives per IIgs, since there is no drive select signal available on pin 9 to the second drive on the chain.
5.25" drives are dumb, they just pass input pin 9 to daisy chain port pin 17. Detecting one or two 3.5" drives connected is likely done by the IIgs firmware. 5.25" don't have auto detection due to their legacy nature.
At the IIgs disk port:
If pin 4 is grounded on the port, first drive is 5.25" thus no 3.5" drives detected
If pin 4 is not grounded on the port and there is a ground present on some random pin, first drive is 3.5", probe to see if there are two drives
3.5" drive in the chain:
If pin 4 is grounded on daisy chain port, drive is 5.25", route drive select 1 signal to pin 17, only activate if input pin 4 is low from computer.
If pin 4 is not grounded on daisy chain port and there is a ground present on some random pin, drive is 2nd 3.5", route drive select 2 signal from pin 9 to pin 17 (this is how the drive avoids receiving the damaging PWM signal on a compact Mac, it never makes it to the floppy drive to begin with!)
If pin 4 is not grounded and there is no ground present on some random pin, drive is last in chain
This configuration only supports 2x3.5" drives per IIgs, since there is no drive select signal available on pin 9 to the second drive on the chain.
5.25" drives are dumb, they just pass input pin 9 to daisy chain port pin 17. Detecting one or two 3.5" drives connected is likely done by the IIgs firmware. 5.25" don't have auto detection due to their legacy nature.