![](http://datasheet.mmic.net.cn/390000/SYM53C876_datasheet_16836340/SYM53C876_32.png)
1-4
SYM53C876/876E Data Manual
Introduction
Wide Ultra SCSI Benefits
split driver architecture that increases system effi-
ciency by transferring I/O-intensive processing
tasks from the host CPU to intelligent peripheral
platforms.
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 mega-transfers per second during an
I/O operation, which results in approximately
doubling the synchronous transfer rates of Fast
SCSI. The SYM53C876 can perform Ultra SCSI
synchronous transfers at 20 MB/s. It can also per-
form Wide Ultra SCSI transfers at 40 MB/s. This
advantage is most noticeable in heavily loaded sys-
tems or large-block size applications such as video
on-demand and image processing.
Another advantage of Wide Ultra SCSI is that it
significantly improves SCSI bandwidth while pre-
serving existing hardware and software invest-
ments. The SYM53C876 is compatible with all
existing SYM53C875 software.
SCSI TolerANT Technology
The SYM53C876 features TolerANT technol-
ogy, which includes active negation on the SCSI
drivers and input signal filtering on the SCSI
receivers. Through active negation, the SCSI
Request, Acknowledge, Data, and Parity signals
are actively driven high rather than passively
pulled up by terminators. Active negation is
enabled by setting bit 7 in the STEST3 register.
TolerANT receiver technology improves data
integrity in unreliable cabling environments,
where other devices are subject to data corrup-
tion. TolerANT receivers filter the SCSI bus sig-
nals 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 SYM53C876 and all Sym-
bios Logic Fast SCSI and Ultra SCSI devices.
The benefits of TolerANT include increased
immunity to noise on the deasserting signal edge,
better performance due to balanced duty cycles,
and improved Fast SCSI transfer rates. In addi-
tion, 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 pro-
tected from data corruption. TolerANT is com-
patible with both the Alternative One and
Alternative Two termination schemes proposed
by the American National Standards Institute
(ANSI).