On Tue, 22 Dec 1998 09:07:03 PST, "Lon Coleman" <lon_c@xxxxxxxxxxx> jammed all
night, and by sunrise was overheard remarking:
> Dave Haynie, if you are attempting to connect a UMAX 1200S to just any
> SCSI chain, you may be disapointed. This scanner will only work with
> SCSI cards with a modest bandwith.
Actually, it works just fine with both of my SCSI cards, one SCSI-2 Wide,
one UltraSCSI. Maybe because I'm a SCSI expert (in a past existance, I
designed SCSI cards).
> If you attempt to connect it to a
> SCSI adapter like the Adaptec 2940UW you will be disapointed (it will
> not work). You can make it works with the 2940UW if you choke the
> 2940UW down to a lower bandwidth via bios settings (but this negates to
> bandwith to all conected devices, so why did you pay so much for a high
> performance SCSI adapter?).
Well, unless there's a bug in the UMAX's SCSI implementation, this isn't
the case. SCSI auto-negotiates between initiator (usually your PC's host
adaptor card) and target (drive, scanner, etc). I don't doubt that the
UMAX's implementation runs only at asynchronous speeds (for the layman,
"SCSI-1" capabilities), it's rarely necessary to make non-hard disc
devices go any faster.
There are some caveats with any SCSI bus (since we're on the subject).
If you don't properly terminate it (and for SCSI-2 and above, that means
active termination, not just the little resistors), it's not likely to
work at all. If you don't observe bus length limits, nothing on the bus
is likely to run at faster speeds (UltraSCSI, for example, is limited to
1.5m total bus length). If you overload the bus, again, you'll suffer in
performance (UltraSCSI typically only supports four total devices, all
other SCSIs physically support 8 devices, the wide versions can, under
circumstances, address 16, though you probably need a bus repeater).
People usually run into trouble with scanners when they run a 6-12'
cable from the PC, to get the scanner over on another desk, then pop on
a passive terminator. Also, if you use the non-approved 25-pin "Mac
style" cables, forget about it. This will kill all faster protocols, but
even sometimes SCSI-1 doesn't work with it, this was never an approved
part of any SCSI specification, and it shows.
> If you stay with a SCSI adapter that does not exceed SCSI II, most
> likely you will be OK. Some other higher performance adapters may work
> (but they are a gamble).
Again, SCSI always starts out slow and at 8-bit, it negotiates for the
faster (synchronous) speeds and wider bus widths (16-bit or 32-bit,
though 32-bit, while in the spec, is virtually unknown).
>
> I have no knowlege about this scanners accomidation of NT.
The problem I had with the UMAX 1200S was only with the SCSI-1 card that
UMAX supplies with the scanner, not with any of my higher performance
devices. Most of the included SCSI cards with these things are
throw-aways, provided simply because SCSI isn't standard on the PC. The
card in question, a total no-name card, totally programmed I/O (that's
bad), simply didn't work reliably enough in Windows NT to be accepted (
it constantly dropped whole lines during transfers). Switching to the
Symbios chip solved the problem, though the scanner eventually wound up
on the Windows 95 machine anyway.
--
Dave Haynie | V.P. Technology, Met@box Infonet, AG | http://www.metabox.de
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