tashtari
PIC Whisperer
So without going into too much detail, I have a slightly mad idea involving bitbanging the Mac floppy interface from a PIC, and I kind of want to know how mad it is.
By way of background, the Mac uses the "phase" lines on the IWM/SWIM chip (originally intended for controlling the drive head's stepper) along with the head select line to demultiplex up to 16 one-bit signals, the floppy drive returning the value of the signal on the read line (its sole line of communication to the Mac).
What I'm wondering is, how fast does the drive have to respond to the Mac changing the select lines in order that the Mac reads back the signal it wants? Is there a limit to how fast the IWM/SWIM chip can be accessed on the bus that might provide a clue?
Such is the complexity of the floppy drive interface that talking to it with programmable logic is possible but cumbersome - if it's tolerant enough of slow communication, the programmable logic might be replaceable with a sufficiently fast and sufficiently cleverly-programmed microcontroller...
Paging @bigmessowires - this might be relevant to your interests - but I'd be happy to hear from any of the many people with better knowledge of Mac innards than I. Anyone? Bueller?
By way of background, the Mac uses the "phase" lines on the IWM/SWIM chip (originally intended for controlling the drive head's stepper) along with the head select line to demultiplex up to 16 one-bit signals, the floppy drive returning the value of the signal on the read line (its sole line of communication to the Mac).
What I'm wondering is, how fast does the drive have to respond to the Mac changing the select lines in order that the Mac reads back the signal it wants? Is there a limit to how fast the IWM/SWIM chip can be accessed on the bus that might provide a clue?
Such is the complexity of the floppy drive interface that talking to it with programmable logic is possible but cumbersome - if it's tolerant enough of slow communication, the programmable logic might be replaceable with a sufficiently fast and sufficiently cleverly-programmed microcontroller...
Paging @bigmessowires - this might be relevant to your interests - but I'd be happy to hear from any of the many people with better knowledge of Mac innards than I. Anyone? Bueller?