Compaq DWZZH - Manual (Page 13)

EK–DWZZH–UG. D01 1–1
1
Introducing the DWZZH UltraSCSI Hub
This chapter describes the DWZZH Hub functions and available versions, and list the
Hub functional specifications.
The series of DWZZH Hubs are SCSI–2 and draft SCSI–3
(ANSI X379.2/91–10R3) compliant 16-bit converters capable of data transfer
rates of up to 40 Mbytes per second. The series of Hubs consists of the following:
•
DWZZH–21 and DWZZH–03 are 3.5" SBB (small) Hubs; the DWZZH–21
contains two single-ended and one differential UltraSCSI ports, while the
DWZZH–03 contains three differential UltraSCSI ports.
•
DWZZH–05 is a 5.25" SBB (large) Hub that contains 5 differential
UltraSCSI ports.
1.1 UltraSCSI Hub Functions
Most device SCSI buses are either 8-bit or 16-bit single-ended, physical buses.
Some controllers and hosts use differential buses and others use a single-ended
bus. Single-ended and differential physical buses are not compatible. The SCSI
protocol disables both buses when they are connected together. However, by
using an UltraSCSI Hub you can accomplish the following:
•
Connect a differential physical bus to a single-ended physical bus
(DWZZH–21 UltraSCSI Hub only).
•
Extend the maximum length of a SCSI bus.
•
Provide radial disconnect where remaining connections can continue to
operate.
•
Provide “fair” SCSI arbitration for host nodes (DWZZH-05 UltraSCSI HUB
only).