LSI LSI53C896, Technical Manual

Page: 21 / 370

TolerANT
®
Technology 1-5
reliability of HVD SCSI without the added cost of external differential
transceivers. Ultra2 SCSI with LVD allows a longer SCSI cable and more
devices on the bus, with the same cables defined in the SCSI-3 Parallel
Interface standard for Fast-20 (Ultra SCSI). 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 LSI53C896
features universal LVDlink transceivers that can support LVD SCSI, SE,
and HVD modes. The LVDlink technology also supports HVD signaling
in legacy systems, when external transceivers are connected to the
LSI53C896. This allows the LSI53C896 to be used in both legacy and
Ultra2 SCSI applications.
1.4 TolerANT
®
Technology
The LSI53C896 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. Active negation is enabled by setting bit 7 in
the
SCSI Test Three (STEST3) register.
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 delay 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. TolerANT input signal filtering is a built-in feature of the
LSI53C896 and all LSI Logic fast SCSI, Ultra SCSI, and Ultra2 SCSI
devices.
The benefits of TolerANT technology include increased immunity to noise
when the signal is going HIGH, better performance due to balanced duty
cycles, and improved fast SCSI transfer rates. In addition, TolerANT SCSI
devices do not cause glitches on the SCSI bus at power-up or
power-down, so other devices on the bus are also protected from data
corruption. When it is used with the LVDlink transceivers, TolerANT
technology provides excellent signal quality and data reliability in real
*