Seagate Ultra160 Product Manual page 24

6 SCSI Interface Product Manual, Rev. B
iuCRC protection—The use of CRC to detect DT DATA PHASE data transmission errors during parallel trans-
fers. Contains CRC information covering all bytes transmitted in a SPI information unit.
layer—A subdivision of the architecture constituted by subsystems of the same rank.
linked CDB—A CDB with the link bit in the control byte set to one.
linked command—One in a series of SCSI commands executed by a single task, which collectively make up
a discrete I/O operation. In such a series, each command has the same task identifier, and all except the last
have the link bit in the CDB control byte set to one.
logical connect—Establishes an I_T_L_Q nexus using SPI L_Q information units.
logical disconnect—Reduces the current I_T_L_Q nexus to an I_T nexus.
logical reconnect—Reestablishes an I_T_L_Q nexus from an I_T nexus using SPI L_Q information units.
logical unit—a SCSI target port-resident entity which implements a device model and executes SCSI com-
mands sent by an application client.
logical unit number—A 64-bit identifier for a logical unit.
logical unit option—An option pertaining to a logical unit, whose actualization is at the discretion of the logical
unit implementor.
lower level protocol—A protocol used to carry the information representing upper level protocol transactions.
mandatory—The referenced item is required to claim compliance with a standard.
media information—Information stored within a SCSI device which is non-volatile (retained through a power
cycle) and accessible to a SCSI initiator port through the execution of SCSI commands.
multidrop—A characteristic of the SCSI bus that allows SCSI devices to be connected to the SCSI bus without
disrupting the electrical path between the terminators.
multimode single-ended (MSE)—A signalling alternative for multimode SCSI devices that employs MSE driv-
ers and receivers to allow multimode SCSI devices to operate when SE SCSI devices are present on the bus.
nexus—A relationship between a SCSI initiator port and a SCSI target port, logical unit, or queue tag that
begins with an initial connection and ends with the completion of the associated I/O process. This relationship
is formed as the result of a task.
object—An architectural abstraction or "container" that encapsulates data types, services, or other objects that
are related in some way.
odd parity—Odd logical parity, where the parity bit is driven and verified to be that value that makes the num-
ber of assertions on the associated data byte plus the parity bit equal to an odd number (1, 3, 5, 7, or 9). See
parity bit. If an even number of asserted bits are detected at the receiver, a parity error occurs.
paced transfer—Parallel transfers that transfer information using pacing.
pacing—Use of the ACK or REQ signal as a continuously running clock in combination with the P1 signal to
indicate when data is valid.
packetized—A method of transferring information using SPI information units. See object.
pad field—The portion of a data group that contains pad information.
parallel protocol request—Messages used to negotiate a synchronous data transfer agreement, a wide data
transfer agreement, and set the protocol options between two SCSI devices.
parity bit—A bit associated with a byte that is used to detect the presence of an odd number of asserted bits
within the byte. The parity bit is driven such that the number of logical ones in the byte plus the parity bit is odd.
pCRC field—The portion of a data group that contains pCRC information.
pCRC protection—The use of pCRC to detect DT DATA PHASE.
peer-to-peer protocol service—A service used by an upper level protocol implementation to exchange infor-
mation with its peer.