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Introduction
TolerANT Technology
SYM53C825A/53C825AE Data Manual
1-3
TolerANT Technology
T he SYM53C825A features TolerANT technol-
ogy, 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 ST EST 3 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.
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 the SYM53C825A and all Symbios fast SCSI
devices. On the SYM53C825A, 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.
SYM53C825A Benefits
Summary
SCSI Performance
I
Includes 4K B internal RAM for SCRIPT S
instruction storage
I
SCSI synchronous offset increased from 8 to
16 levels
I
Supports variable block size and scatter/gather
data transfers.
I
Performs sustained memory-to-memory
DMA transfers faster than 47 MB/s (@ 33
MHz))
I
Minimizes SCSI I/O start latency
I
Performs complex bus sequences without
interrupts, including restore data pointers
I
Reduces ISR overhead through a unique
interrupt status reporting method
I
Performs fast and wide SCSI bus transfers in
single-ended and differential mode
I
10 MB/s asynchronous
I
20 MB/s synchronous Load and Store
SCRIPT S instruction increases performance
of data transfers to and from chip registers
I
Supports target disconnect and later reconnect
with no interrupt to the system processor
I
Supports multi-threaded I/O algorithms in
SCSI SCRIPT S with fast I/O context
switching
I
Expanded Register Move instruction supports
additional arithmetic capability
I
Complies with PCI Bus Power Management
Specification (SYM53C825AE) Revision 1.0
PCI Performance
I
Complies with PCI 2.1 specification