14 scsi bus interface, Scsi bus interface – Avago Technologies LSI53C896 User Manual
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SCSI Functional Description
2-35
Version 3.3
Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
register. AND the result with 0x3FF for a
byte count between zero and 944.
Step 2.
Read the
register and examine bits
[7:4], the binary representation of the number of valid bytes in
the SCSI FIFO, to determine whether any bytes are left in the
SCSI FIFO.
Step 3.
If any wide transfers have been performed using the
Chained Move instruction, read the Wide SCSI Receive bit
(
, bit 0) to determine whether a
byte is left in the
register.
2.2.14 SCSI Bus Interface
The LSI53C896 performs SE and LVD transfers, and supports traditional
HVD operation when the chip is connected to external HVD transceivers.
To support LVD SCSI, all SCSI data and control signals have both negative
and positive signal lines. The negative signals perform the SCSI data and
control function. In the SE mode they become virtual ground drivers. In the
HVD mode, the positive signals provide directional control to the external
transceivers. TolerANT technology provides signal filtering at the inputs of
SREQ/ and SACK/ to increase immunity to signal reflections.
2.2.14.1 LVDlink Technology
To support greater device connectivity and a longer SCSI cable, the
LSI53C896 features LVDlink technology, the LSI Logic implementation of
LVD SCSI. LVDlink transceivers provide the inherent reliability of differential
SCSI, and a long-term migration path of faster SCSI transfer rates.
LVDlink technology is based on current drive. Its low output current
reduces the power needed to drive the SCSI bus, so that the I/O drivers
can be integrated directly onto the chip. This reduces the cost and
complexity compared to traditional HVD designs. LVDlink technology
lowers the amplitude of noise reflections and allows higher transmission
frequencies.
The LVDlink transceivers operate in LVD or SE modes. They allow the
chip to detect an HVD signal when the chip is connected to external HVD
transceivers. The LSI53C896 automatically detects which type of signal
is connected, based on the voltage detected by the DIFFSENS pin.