Hi!

I've been trying to decipher how the Mac interfaces with the Suprdrive floppy drive through the ISM part of the SWIM chip. I've almost got it, but I don't understand what the PH0 to PH3 lines are trying to do.

In particular, when the drive is idle, they emit very brief pulses at a rate of about once a second. Why is this?

Thanks,

speedcuber50