[Gllug] SCSI query (LVD and UltraWide compatibility)

[Mike Brodbelt]

On Mon, 2002-01-14 at 00:40, Matt B wrote:
> Hi Martyn
> 
> > I'm contemplating buying the ACARD AEC67160 Ultra160 PCI controller
> > which comes with an internal and external Ultra160 LVD connector (which
> > I understand is a 68 pin connection in the same style of Ultra Wide
> > connectors).  What I want to know is whether I can connect my Ultra Wide
> > devices using either the supplied LVD connector or a normal Ultra Wide
> > connector.  Is LVD backwards compatible with Ultra Wide devices?
> 
> > Sorry to sound a bit blank about this sort of thing, but after all this
> > talk about SCSI, it's made me want to get it on my system and give it a
> > go.
> 
> LVD are 68 pin, as are UltraWide. The AEC67160 supports SCSI-1, SCSI-2,
> SCSI-3, Ultra SCSI, Ultra2 SCSI and Ultra160 SCSI, which means you shouldn't
> have any problems.
> 
> LVD is not directly backwardly compatible with other SCSI standards due to
> it's cable requirements. However if you want to connect LVD devices in the
> same SCSI chain as UW drives then make sure that all the cables on the chain
> are LVD cables, otherwise the lower-voltage-differential won't work.

It won't work anyway, AFAIK. LVD and single ended signalling modes are
fundamentally different - if you want to run stuff in LVD mode you need
an LVD capable controller, drives, and cables. If you stick single ended
kit on the same chain, you'll probably get away with it, but only
because the LVD stuff falls back to SE mode.

Pay attention to drive jumpers if doing this - IBM at least have jumpers
to select SE/LVD mode on some models of their drives, and if you don't
have them set to SE mode when on a SCSI chain with other SE devices
attached, they'll not be detected by the controller at all.

HTH,

Mike.


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