SCSI termination

[Scott Long]

docaia wrote:
> can somebody please explain to me a simple way what is a single ended
> terminator and what is a differential terminator and what is the damage
> which may be caused by putting Single Ended devices on a Differential bus?
> I am a geophysicsit so I don't have a strong electronic backgroud, so
> consider me as a very beginner, and please explain this to me thoroughly.
> thank you

The big issue to watch out for is High Voltage Differential (HVD) vs Low
Voltage Differential (LVD).  They operate at dangerously different
voltage levels, and mixing them together will often cause smoke, fires,
and permanent equipment (and personnel) damage.

Single Ended buses operate at the same voltage as LVD buses, so there is
no danger in mixing them.  The only caveat is that an LVD bus will
automatically downshift to single ended if any single-ended devices are
directly attached to it.  Some adapters will provide both LVD and SE
connectors for the same bus, with an internal converter chip that
prevents the downshift.  Connecting an LVD device to an SE bus poses
no problem.

Putting an SE terminator on an LVD bus will downshift the bus to SE.  I
somewhat recall a conversation about it being unsafe to put an LVD
terminator on an SE bus, but I don't recall the specific reasons.  For
best results just try to keep SE and LVD devices and buses matched and
segregated appropriately, and don't mix HVD with anything non-HVD.

Scott