On 24.05.01, 03:39:17, Andy Ball wrote:
> 
> Hello Bernd!
> 
>   BS> Between Ultra and U160 there's still Ultra-Wide and
>     > Ultra-2-Wide (LVD).
> 
> I was aware of those, but none of the CD-RW drives I looked
> at had a wide SCSI bus.  Perhaps that will change if CD-RW
> manufacturers adopt Ultra160.

Yes, of course. No offense intended.

> 
>   BS> I don't think that differential modes are commonly
>     > used on narrow busses.

I found out that Ultra2-narrow is specified. But I've never seen
it.

> 
> That was my impression too.  I've seen conflicting reports
> about what signalling methods are used with each of the wide
> standards, so I'm having to read the small print on
> everything.  Unfortunately a lot of manufacturers seem to
> omit potentially important information.  :-/

Basically almost everything sold today is up- and
downwards-compatible.

One place where the exact cable lengths and operating modes are laid
out is the WD SCSI drive installation guide:

http://www.wdc.com/acrobat/scsi/SCSI-IG.pdf

(I am not affiliated with WD, in fact I don't even have a single WD
device. I just found that document to be useful.)

> 
> Perhaps I should tell him to hold off until CD-RW makers
> release Ultra160 drives then, in the interests of
> consistency and simplified cabling.

Connecting a narrow device to a wide bus is not really a problem with
an adaptor (should be less than $10 if you find a good dealer. Can be
up to $40(!), if you don't), if the (wide) cable continues on after
the narrow drive and is properly terminated.

The only problem is that the bus cannot operate any faster than at
Fast-20 (Ultra) speed. (I. e. no LVD).

> 
>   BS> I have a Tekram DC-390F (Ultra Wide, 16Bit, 20 MHz),
>     > based on Symbios 53C875, and now there are 2 disks,
>     > CD-R and DVD-ROM on the narrow connector, and one disk
>     > on the wide connector.
> 
> Are the narrow and wide connectors segments of the same bus,
> or separate busses? Either way, it's another option to

One bus. Dual channel host adaptors (like the Adaptec 3940 series and
Tekram DC-390-U3W and -U3D) are usually a lot more expensive.

> consider. The only disadvantage that springs to mind is
> having to run two cables.  What signalling are you using on

The second disadvantage is that you cannot use the external connector,
since that would create an illegal "Y"-topology on the bus.

> the wide connector: S/E, HVD or LVD?

S/E. Since it's the same bus as the narrow connector, I'm forced to
use single ended operation.

> 
> Regards,
>   - Andy.
> 

-- 
Bernd Sieker

NetBSD, SIMMs Like Good Code
		-- Andrew Gillham