Avago Technologies LSI53C876E - Manual (Page 18)

1-4 General Description
1.1 Wide Ultra SCSI Benefits
Wide Ultra SCSI is an extension of the SCSI-3 family of standards that
expands the bandwidth of the SCSI bus and allows faster synchronous
SCSI transfer rates. When enabled, Wide Ultra SCSI performs
40 megatransfers per second during an I/O operation, resulting in
approximately twice the synchronous transfer rates of Fast SCSI. The
LSI53C876 can perform Ultra SCSI synchronous transfers at
20 Mbytes/s. It can also perform Wide Ultra SCSI transfers at
40 Mbytes/s. This advantage is most noticeable in heavily loaded
systems or large block size requirements, such as video on-demand and
image processing.
An advantage of Wide Ultra SCSI is that it significantly improves SCSI
bandwidth while preserving existing hardware and software investments.
The LSI53C876 is compatible with all existing LSI53C875 software.
1.2 TolerANT
®
Technology
The LSI53C876 features TolerANT technology, which includes active
negation on the SCSI drivers and input signal filtering on the SCSI
receivers. Active negation actively drives the SCSI Request,
Acknowledge, Data, and Parity signals HIGH rather than allowing them
to be 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
LSI53C876 and all LSI Logic Fast SCSI and Ultra SCSI devices.
The benefits of TolerANT technology include increased immunity to noise
on the deasserting signal edge, 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