8" disk drive project

[Grant Stockly]

I want to use a QUME 842 or SA800 in an altair disk subsystem.

Both seem to have the same interface.

The FD400-5x0-5x1 manual seems to show the drives being quite similar.

The first thing I see is that there are extra signals.

"Trim Erase", "Write Enable", and "Write Data" where the Shugart 
interface only has "Write Data" and "Write Gate".  I assume that gate 
and enable are the same thing.  The FD Pertec drives also have "IN", 
"OUT", and "STEP" instead of "STEP" and "DIRECTION", but that is not 
a big deal.  That can be generated in software.

What I don't see is any input to perform the function of head 
current.  How does the shugart interface handle this?

Can I ignore the trim erase feature?  How do I generate a write busy 
signal?  I'm willing to make some circuits to fake these signals if required.

Thanks,
Grant