SCSI Multidrop Bus Topology
Interface Interface Interface
• Varieties include Fast, Fast Wide, Ultra, and Ultra-3
• Bandwidth ranges from 5MB/s to 320MB/s
• Supports up to 16 devices attached to the bus
• Data/address bus is 8 bit or 16 bit (WIDE) plus parity
• Interface is Single Ended (SE), 5volt (HVD) or 3volt (LVD)
• Maximum distance is from 1.5 metres to 25 metres depending
Parallel bus architecture shares the use of the bus for both data bits and
Only one function (addressing or data) can be present on the bus at any
one time, so the bus divides the available time or cycle into phases.
These phases are called the address phase, the data phase. Sometimes
there is also a control phase.
SCSI devices utilize hard addressing:
Each device has a series of jumpers which determine their physical
address or ID. The ID is sometimes software-configurable.
Each device must have a unique ID. Before adding a device to the
cable, the administrator must know the ID of every other device
connected to the cable and choose a unique ID for this new device.
IDs determine priority on the bus, so the SCSI initiator with ID 7 has a
higher priority than the SCSI target with ID 0.