#SOMY MAGNETO HELP!
7 messages in this thread
Fellow (and probably more experienced) Amiga users,
I am considering purchasing a Sony Magneto-Optical SCSI Drive. The
unit is currently being used on a 486 IBM system, but SCSI is SCSI, so
it'll function for me. My question is this, will I need a special driver
for the unit, or will my GVP Combo board software handle the I/O setup for
me? Additionally, the SCSI connectors on the back of the are not D
connectors, like the rear of my GVP board. They appear to be
centronics-style (like a parallel printer). Is there a conversion cable
available? If so, where?
Any help would be fantastic.
ERIC
Eric:
The Sony drive should work with no problem. No special drivers are needed
as long as it's a read/write drive. If it's a WORM drive I'm not sure the
Amiga can handle it, but I'm not really sure. The centronics connector is
actually the SCSI standard, a 50 pin Amphenol (the more correct name for
the connector) connector. The Mac & Amiga both seem to have gone to a 25
pin connector instead, and there are plenty of places to get a 25pin D to
50 pin Amphenol cable.
-Mike Schiller
In sunny Fort Lauderdale
Mike,
Thank you for the info on the connector types, as I found out after
posting my original message, SCSI is actually only 25 pin, and on the
Amphenol connector, one whole side is merely chassis ground!
As far as the drive goes, its a Magneto-Optical (removeable media)
drive. Each "disk" gives you 300MB per side, for a total of 600MB per
disk. They are Read/Write, not WORM. Instead of using a magnetic "head"
to arrange all the 1's and 0's, it uses light.
Thanks
ERIC
Actually, SCSI is 50 pins. The 24 ground lines (pin 25 is open) are part
of the specification.
Craig
And — just to make things really interesting — there is another "flavor"
of SCSI where those 24 "ground lines" cease to become ground lines and
actually carry 1/2 of the data signal. "Differential" SCSI isn't too much
used, but if you need _long_ (25 or so feet) cable runs it works well.
– via Whap!
Brian,
Single-Ended SCSI uses a voltage swing of 5v for it's signals
(signals are either 0v or +5v) and has a maximum (by spec) cable length of
6 meters (19' 8"). Differential SCSI on the other hand only cares if the
+signal is more positive than the -signal. Differential SCSI cables may be
up to 25 *meters* (82 feet) in length.
By the way, as an aside to those reading this thread and asking why
their drives work if there's too many terminators in the chain, it's
because of the design of termination and the signal levels allowed.
Terminators look like this:
+5v line————–+
|
220 ohm resistor
|
signal line———–+
|
330 ohm resistor
|
ground line———–+
The spec calls for a signal line to be asserted (binary 1) if it's
voltage level is between 0 and 0.4v and not asserted (binary 0) if it's
voltage is between 2.5v and 5v.
With both ends terminated like this…electrically it's as if, in
total, there were a 110ohm resistor between 5v and the signal line and a
165 ohm resistor between the signal and ground. By adding a 3rd terminator
array in the system, the values drop to 73 ohms and 110 ohms. The ratio
between the two resistances says a constant 2:3 even with the extra
termination. But what does change is current characteristics of the line.
Since 0 volts on the signal line is a bianry 1…the SCSI device
has to bring that line to ground to assert it. In other words, it has to
"sink" the current on the line. So by adding more terminators…it has to
sink more power. In other words…it'll work, but you're drawing more
current (thus more heat) and can more easily burn out the driver circuitry.
Make sense?
Don
Eric:
If it's similiar to the Ricoh magneto-optical drive I just sold, then no
special driver is nessasary. The one thing I will tell you is that it
takes a LONG time to do an AmigaDOS format on each partition (about 45
minutes on the Ricoh).
Yes, on an Amphenol connector half of the leads are grounds, but they are
also part of the SCSI spec so the DB25 connector isn't a 'proper'
connector for SCSI, even thou both Macs and Amigas use them as such.
-Mike Schiller
In sunny Fort Lauderdale