You're one incredible genius of the luck !
I'm someone who like to understand obscur things, and I smiled a bit when I've finally got what you've done.
Yes, curiously, inverting pin 2 and 34 will make an x68000 floppy drive to work on regular PC, but not because of the way you understand it.
First, to make some points :
- Shugart is an interface, not a bus.
- Only SA400 series floppy drives from Shugart Associates are 34 pins, which is the drive that serve as base for IBM. But on SA400, there is no Disk Change or Ready or Density select signals at all. (See SA400 datasheet page 12)
- I've never heard about a disk change or ready signal on IBM pin 2 ! If it was the case with your 486, you will not be able to use common drives !
- As I said, the x680x0 floppy drives use READY signal on pin 34, and density select on pin 2. (See CZ-600CE schematics, peripherals page)
- PC use DISKCHANGE on pin 34, and density select on pin 2. (See any floppy drive datasheet, I've used Samsung SFD321B)
Now, here are involved signals descriptions :
- READY : the drive must tie this line to a "low" level to indicate that a media is inserted, and motor up to its maximum speed.
- DISKCHANGE : the drive tie this line to a "low" level to indicate that the media have changed since the last host query. If the media has not changed, it stays to "high" level.
- Density Select : we have different behavior here between the x680x0 and PC :
* PC (expecting configured as 3mode) : "high" level means a 2.0MB media is inserted. "low" level is for 1.6MB. (As reminder, x68000 floppies are 1.6MB)
* X680x0 : "high" level when the drive is 5.25'. "low" level for a 8' floppy drive. (never seen a 8' drive for this machine... but well)
That means, assuming a floppy is inserted into an x68000 drive, it will always send "high" on pin 2 (5.25' drive) and "low" on pin 34 (drive ready).
Wired like this on a PC means that the media keeps changing, and btw... is 2.0MB.
But by inverting these two signal, the PC will see that the media is still the same, and is 1.6MB !
So, what you did is totally wrong in theory ! But will make the thing totally work in practice !
A note for users who wish to do this trick : it's safe, but be sure to correctly prepare a ribbon cable by cutting wires 1,3,5,7,9,11,13,15,17 and 19. Then cross wires 2 with 34. Also, it's better to insert a disk before powering your PC !
A picture of your cable could be nice doubleflash.