Hi all,
So today I have begun the effort of designing a floppy drive controller and have a question about data storage.
I have done a tonne of research and have print-outs of old documentation (so I am not being lazy ). I connected up the floppy drive pins (34 of them) to their needed IO levels and sure enough, I could get the motor spinning, get the track 0 signals pulsing and read / write data to the floppy.
I do understand that FM is needed to store data (as the data is encoded not stored) because a change in magnetic field is what is recorded. But here is something I don't understand:
If I take a 500KHz square wave and feed this into the write pin then read the data I can clearly see the 500KHz wave. If I modulate this with some other square wave again I can see this from the output. What I don't understand is that if I hold the write pin high or low the data is left unchanged on the floppy. Is there some kind of AC coupling on the input pin? Surely if I hold this pin high or low the magnetic field produced should just align all the poles in some direction and result in the output to be totally flatlined?
All the best,
Robin
So today I have begun the effort of designing a floppy drive controller and have a question about data storage.
I have done a tonne of research and have print-outs of old documentation (so I am not being lazy ). I connected up the floppy drive pins (34 of them) to their needed IO levels and sure enough, I could get the motor spinning, get the track 0 signals pulsing and read / write data to the floppy.
I do understand that FM is needed to store data (as the data is encoded not stored) because a change in magnetic field is what is recorded. But here is something I don't understand:
If I take a 500KHz square wave and feed this into the write pin then read the data I can clearly see the 500KHz wave. If I modulate this with some other square wave again I can see this from the output. What I don't understand is that if I hold the write pin high or low the data is left unchanged on the floppy. Is there some kind of AC coupling on the input pin? Surely if I hold this pin high or low the magnetic field produced should just align all the poles in some direction and result in the output to be totally flatlined?
All the best,
Robin