8 May
2007
8 May
'07
2:30 a.m.
Chuck Guzis wrote:
I don't think there's anything that can't
be handled with a DC-37
connector--and that's with 4 drive selects. You don't need the
separated data from 8" drives, so let's look at what signals you do
need:
DS0
DS1
DS2
DS3
MOTOR ON or HEAD LOAD*
SIDE SELECT
INDEX
TRACK 0
STEP
DIRECTION
READ DATA (RAW)
WRITE DATA
WRITE GATE
WRITE PROTECTED
SECTOR (if you want to use the 8" signal)
TG43
*Saying that both HDLD and MTRON are the same signal simplifies
accommodating 8" drives and doesn't hurt a thing.
Some drives have speed control on one of the pins (300/600 RPM, or 300/360
RPM), LED signal, motorised eject, disk change reset etc. - I suspect that it
doesn't hurt to have a few I/O lines set aside on the interface connector for
special cases.
Not to mention some drives getting power over the 'data' cable, but the less
said about those the better :-)
16 signal lines + return = 32 pins. Some NEC
3.5" floppies have some
very strange "extra" signals, but they're the only ones I'm aware of.
Similarly, some early 8" drives wanted 3-phase stepping signals, but
I haven't seen a specimen in the last 20 years. Similarly, there are
drives with door locks and auto-ejects that can be ignored.
I'm not sure that ignoring the less-common cases is a good idea though, simply
because *everything* is becoming less common now. I was amazed at how
difficult it was to find a 5.25" HD drive recently; they've all but vanished
despite being so common in PCs at one time. I expect getting a 5.25" 40T drive
is even harder for a lot of people.
There's no point to using the 8" drive
on-board FM data separator.
Why complicate things? Two DC-37 connectors will allow you to
control 8 drives and yet keep the cabling simple.
Wouldn't you have to have motors running on four drives at once, though? I'm
not sure that it matters in practice though as for an archival box I suppose
you only have one disk in one of the drives at any one time...
Generally write precompensation isn't used in FM
mode.
[snip]
Now that was interesting stuff... thanks.
cheers
Jules