steve573 said:
Hi Everybody,
I have a 35mm film scanner which I used to use with XP via a SCSI card
connection to the PC tower (that is the only output from the scanner).
Obviously my new Powerbook G4 hasn't either the room or compatibilty
to connect the scanner to it as designed and so as I no longer have a
PC the film scanner is now effectively useless to me. That is until
surfing away on ebay I saw some scsi to usb adapter cables. On the
face of it these seem the answer to my problems but the ones I can
find have the long flat SCSI type connections to them but my SCSI
output is to a DB25 type cable and I can only find straight DB25 to
USB cables online without any conversion electronics in them (as the
other 50 pin ones do). So my 2 questions are:
1/. Would anybody know if there exists a SCSI DB25 to USB cable
adapter??
2/. If they do exist do these things work??
I intend to use Vuescan software to talk to the scanner if it helps
the answers given (if any!!).
Thanks in advance for any help/advice,
Steve.
Example of a USB to SCSI adapter. One advert claimed the max transfer
rate is 1.2MB/sec, which is almost a USB 1.1 interface rate (i.e. not
taking advantage of USB 2.0). That transfer rate is low enough, to
perhaps cause your scanner to enter start/stop mode (scanner stops
while data buffer empties, increasing scan time).
http://www.coolgear.com/images/326605pro.jpg
The DB-25 option is something that Apple used to use. Typically this
is Async SCSI and 8 bit, running at a pretty low speed (5M/sec to 6M/sec,
with max speed proportional to cable length, due to how data strobing
works). Old scanning devices are seldom cable limited, and my scanner
with Mac DB-25 interface runs between 1 and 2MB/sec. The Coolgear example,
looks to have a DH50 connector.
http://www.datapro.net/techinfo/scsi_doc.html
Here is the pinout for the DB-25, as compared to 50 pin SCSI. Fortunately
both are 8 bit (narrow) SCSI, so there are no extraordinary termination
requirements. (The termination scheme you are already using should be
enough, as long as something is supplying the +5V TERMPWR.)
http://www.umich.edu/~archive/mac/misc/documentation/scsicase1.1.txt
This is an example of a more fully specified product. Notice that it
specifically mentions Async SCSI as an operating mode. Why the command
set should matter, bothers me a bit. All that should matter, is the
ability for USB to transfer the CDB (command/data block) to the SCSI device.
This device apparently has firmware inside, and the advert says it
supports neither SCSI scanner nor SCSI printer command set. Hmmm...
http://www.synchrotech.com/product-usb/usb2-uscsi-conv_01.html
Maybe we should go back to square one. Your computer is a Powerbook G4.
Maybe a PC Card adapter would be a better bet, as that will appear
as a genuine SCSI bus to MacOSX as long as a driver is available.
(For example, I have an old desktop Mac, and it has support for the
Adaptec 2906 built into MacOSX, and my scanner works fine with it.
It still takes a few tricks, but that is the Mac for you.)
This Ratoc product is getting closer to where we want to be.
http://www.synchrotech.com/products/scsi-io-pcmcia-cardbus_01.html
http://www.ratocsystems.com/english/products/CB31pismo.html
There are some Async devices listed in this Ratoc compatibility list,
so Async capability also seems to exist on the CB31PB.
http://www.ratocsystems.com/english/support/Compatible/cb31p_compatibility.html
The cabling would still appear to be a mess! Consult the bottom of
this page, for some adapter options.
http://www.ratocsystems.com/english/products/CB31pismo.html
Perhaps a call to Synchrotech would clear up whether all that is
needed is the RCL-3004-05 "D-Sub 25 cable for CB31Pismo".
http://www.ratocsystems.com/english/about/wtb.html#USA
It is still not clear to me, where TERMPWR comes from with this
setup. The Cardbus appears to run from 3.3V. I don't know if a
Cardbus slot has access to +5V, as 5V is needed to drive the
TERMPWR pin. For Async SCSI, the terminator down at the SCSI
scanner end of your SCSI chain, might look like this. The
resistors are inside the terminator block. On my setup, my passive
terminator is down at the scanner end, and is a Centronics 50P type.
I presume +5V is on pin 25 of the DB-25 end, as my setup does work.
+5V ----- 220 ohm -----+------ 330 ohm ------ GND
TERMPWR resistor | resistor
|
To each high speed bus signal
at the last SCSI device
on the chain.
I suppose the fact that they supply a DB-25 cable, implies they've
taken care of it. Maybe I'm just worrying too much. And since this
is not a hard drive, it is not like something can get corrupted
if TERMPWR is missing.
I expect fighting with a Cardbus SCSI adapter is going to be more
productive, than attempting to get the USB version to do it.
Have fun,
Paul
