Communicator e3000 MPE/iX Release 7.0 Express 1 (Software Release C.70.01) (30216-90328)

66 Chapter4
PCI-SCSI Device Adapter Cards
PCI-SCSI Device Adapter Cards on HP e3000 N-Class and A-Class Systems.
referred to as “Fast/Wide SCSI” or F/W SCSI. These devices are connected via a 68 pin
cable with 16 data bits (2 bytes) and use a +-5 volt differential signal to communicate at up
to 20 Mbytes per second. The term “Fast-Wide SCSI” is actually incomplete in defining
the type of device being used; a more proper term would be High Voltage Differential SCSI
(HVD) using Fast Wide signaling. Examples of these HVD devices include the DLT7000
Tape drive, numerous “Fast-Wide” Disks such as the HPC2490WD or ST39173WD, all of
which are typically connected to the HP28696A Fast/Wide SCSI Adapter Card. On the
N-Class and A-Class systems, HVD devices are supported via connection to A4800A and
A5159A PCI-SCSI Device Adapter Cards.
With the introduction of the N-Class and A-Class Systems, there is a new type of SCSI
device available known as Low Voltage Differential (LVD) Devices. These devices are
connected via a 68 pin cable with 16 data bits (2 bytes) and use a +-3.3 volt differential
signal to communicate at up to 80Mbytes per second. As of the time that this article is
written there are no fully LVD devices being supported on the HP e3000. The SCSI
standard states that all LVD devices should have the capability of operating in SE-SCSI
mode. Thus, the LVD Device Adapters that HP supports have the capability to support
both Single-Ended and LVD devices. This means that it is possible for older SE-SCSI
devices to be used with an LVD Device Adapter (though they will transfer data at the
lower SE-SCSI rate). On the N-Class and A-Class systems, LVD devices would be
supported via connection to A5149A and A5150A PCI-SCSI Device Adapter Cards.
Physical Connectors and Cables
With these different electrical characteristics, there are also different physical connectors.
At this time HP supports devices that use four different types of physical connectors: Low
Density (LD) 50-Pin (example DDS-2 C1530B), High Density 50-Pin (HP28642A Device
Adapter Card), High Density (HD) 68-Pin (HP28696A Fast/Wide SCSI Adapter Card) and
Very High Density (VHDCI) 68-pin (A5149A, Single Port Ultra 2 SCSI (PCI bus) Adapter
Card). This means there are a large number of cable types in varying lengths, some with
different connectors on each end (LD50 -> HD50 or HD50 -> HD68 or HD68 -> VHDCI68,
etc.) When ordering cables pay particular attention to the type of connectors present on
each device you are connecting.
The type of physical connector does not explicitly dictate the type of electrical signals that
can be used. For instance SE, HVD and LVD signals can all be transmitted through a
68-pin cable with High Density connectors, but NOT at the same time! Hooking up SE
devices to HVD devices (or vice versa) can actually damage the devices; so be cautious.
Just because you can physically connect doesn’t mean that you should. (The complexity of
this issue is one reason that we recommend that all peripheral installation be done by HP
Technicians.)