Avago Technologies LSI53C180 - Manual (Page 17)

Ultra160 SCSI 1-7
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 find 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 Benefits of LVD Link
The LSI53C180 supports LVD technology for SCSI, a signaling
technology that increases the reliability of SCSI data transfers over
longer distances than those supported by SE 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 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.
For backward compatibility to existing SE devices, the LSI53C180
features multimode LVD Link transceivers that can switch between LVD
and SE modes.