Avago Technologies LSI53C180 - Manual (Page 21)

Interface Signal Descriptions 2-3
device is taken from the MSG bytes during negotiation. For all devices
in the configuration to communicate accurately through the LSI53C180
at Ultra160 (Fast-80) rates, it is necessary for a complete synchronous
negotiation to take place between the initiator and target(s) prior to any
data transfer. On a 16-bit bus, the LSI53C180 at Ultra160 approaches
rates of 160 Mbytes/s. The LSI53C180 defaults to Fast-20 rates when a
valid negotiation between the initiator and target has not occurred.
2.1.1.2 TolerANT Technology
In SE mode, the LSI53C180 features TolerANT technology, which
includes active negation on the SCSI drivers and input signal filtering on
the SCSI receivers. Active negation causes the SCSI Request,
Acknowledge, Data, and Parity signals to be actively driven HIGH rather
than passively pulled up by terminators.
TolerANT receiver technology improves data integrity in unreliable
cabling environments, where other devices would be subject to data
corruption. TolerANT receivers filter the SCSI bus signals to eliminate
unwanted transitions without the long signal delays associated with
RC-type input filters. This improved driver and receiver technology helps
eliminate double clocking of data, the single biggest reliability issue with
SCSI operations.
The benefits of TolerANT technology include increased immunity to noise
on the deasserting signal edge, better performance due to balanced duty
cycles, and improved SCSI transfer rates. In addition, TolerANT SCSI
devices prevent glitches on the SCSI bus at power-up or power-down, so
other devices on the bus are also protected from data corruption.
2.1.1.3 LVD Link Technology
To support greater device connectivity and longer SCSI cables, the
LSI53C180 features LVD Link technology, the LSI Logic implementation
of multimode LVD SCSI. LVD Link transceivers provide the inherent
reliability of differential SCSI, and a long-term migration path of faster
SCSI transfer rates.
LVD Link technology is based on current drive. Its low output current
reduces the power needed to drive the SCSI bus. Therefore, the I/O
drivers can be integrated directly onto the chip. This reduces the cost and
complexity compared to traditional (high power) differential designs.