
Introduction
TolerANT Technology
1-2
SYM53C810A Data Manual
SYM53C810A increases SCRIPT S performance
and reduces PCI bus overhead by allowing instruc-
tion prefetches of four or eight dwords.
Software development tools are available to devel-
opers who use the SCSI SCRIPT S language to
create customized SCSI software applications. T he
SYM53C810A allows easy firmware upgrades and
is supported by advanced SCRIPT S commands.
TolerANT Technology
All Symbios Logic Fast-SCSI devices feature Tol-
erANT technology, which includes active nega-
tion on the SCSI drivers and input signal filtering
on the SCSI receivers. Active negation causes the
SCSI Request, Acknowledge, Data, and Parity sig-
nals to be actively driven high rather than passively
pulled up by terminators. Active negation is
enabled by setting bit 7 in the ST EST 3 register in
the SYM53C8X X family products.
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.
T his 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 all Symbios Logic fast SCSI devices. On the
SYM53C8X X family products, the user may select
a filtering period of 30 or 60 ns, with bit 1 in the
ST EST 2 register.
T he benefits of TolerANT 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. TolerANT is compatible with both the
Alternative One and Alternative Two termination
schemes proposed by the American National Stan-
dards Institute.