Ultra3 SCSI
1-7
All single bit errors, two bits in error, or other error types within a single
32-bit range are detected. Refer to SPI-3 to see how CRC generation
and transmission occur during data transfers.
1.2.3 Domain Validation
Domain Validation is a procedure that allows a host computer and target
SCSI peripheral to negotiate and nd the optimal transfer speed. This
procedure improves overall reliability of the system by ensuring integrity
of the data transferred.
1.2.4 Parallel Protocol Request
Parallel Protocol Request (PPR) messages negotiate a synchronous
data transfer agreement, a wide data transfer agreement, and set the
protocol options between two SCSI devices. This message exchange
negotiates limits about data transmission and establishes an agreement
between the two SCSI devices. This agreement applies to ST Data In,
ST Data Out, DT Data In, and DT Data Out phases.
For example, a SCSI device could initiate a PPR message whenever it
is appropriate to negotiate a data transfer agreement. If the target device
is capable of supporting any of the PPR options, it will respond with a
PPR message. If not, it responds with a Message Reject message and
the two SCSI devices use either SDTR or WDTR messages to negotiate
an agreement.
1.2.5 Benets of LVD Link
The SYM53C180 supports Low-Voltage Differential (LVD) technology for
SCSI, a signaling technology that increases the reliability of SCSI data
transfers over longer distances than those supported by single-ended
SCSI technology. The low current output of LVD allows the I/O
transceivers to be integrated directly onto the chip. LVD provides the
reliability of High-Voltage Differential (HVD) SCSI technology without the
added cost of external differential transceivers. LVD allows a longer SCSI
cable and more devices on the bus. LVD provides a long-term migration
path to even faster SCSI transfer rates without compromising signal
integrity, cable length, or connectivity.