Avago Technologies LSI53C320 - Manual (Page 26)

2-8 Functional Descriptions
Version 2.2 Copyright © 2003 by LSI Logic Corporation. All rights reserved.
When the DIFFSENS voltage selects SE mode, the LSI53C230 internally
ties the plus signals to ground and the minus SCSI signals become the
SE input/outputs. When the DIFFSENS voltage selects LVD mode, the
plus and minus signals are the differential signal pairs.
Any dynamic mode change (SE-to-LVD or LVD-to-SE) on a bus segment
is a significant event, and the initiator must determine if the new bus
mode meets the requirements for the bus segment. The LSI53C320
supports dynamic transmission mode changes by notifying the initiator(s)
of changes in the transmission mode with a SCSI bus RESET/. The
DIFFSENS line detects a valid mode switch on a bus segment. After the
DIFFSENS state is continuously present for 100 ms, the LSI53C320
generates a SCSI reset on the bus opposite the bus on which the
transmission mode change occurred. This reset informs initiators residing
on the opposite bus segment of the change in the transmission mode.
The initiator(s) then renegotiates synchronous transfer rates with each
device on that segment.
If the LSI53C320 detects the HVD mode on a SCSI bus segment, the
LSI53C320 3-states its outputs.
2.2.2.2 SCSI Termination
The terminator networks pull signals to an inactive voltage level and
match the impedance seen at the end of the cable with the characteristic
impedance of the cable. Install terminators at the ends of each SCSI
segment, and only at the ends; all SCSI buses must have exactly two
terminators.
2.2.3 Maximum Cable Lengths
The electrical length of a bus is the time required for round-trip signal
propagation between bus ends. This section discusses the maximum
electrical and physical cable lengths when cascading LSI53C320
Table 2.1 DIFFSENS Voltage Levels
Mode Voltage
SE
−
0.35 to +0.5
LVD +0.7 to +1.9