Avago Technologies LSI53C320 - Manual (Page 28)

2-10 Functional Descriptions
Version 2.2 Copyright © 2003 by LSI Logic Corporation. All rights reserved.
Figure 2.4 Electrical Cable Lengths at Ultra320 SCSI Speeds
2.2.3.2 Maximum Physical Cable Length
Table 2.2 provides information concerning the maximum physical cable
length when operating the LSI53C320 at Ultra320 SCSI transfer rates.
The SPI-4 standard allows a maximum point-to-point physical cable
length of 25 m and a maximum fully loaded physical cable length 12 m.
This limits the total physical cable length to 37 m. To allow for board
capacitance and signal propagation through the expander, LSI Logic
recommends limiting the point-to-point physical cable length to 20 m.
This limits the total physical cable length to 32 m.
Table 2.2 provides the total maximum cable length depending on the
number of expanders that are cascaded on the bus. As long as the total
cable length between expanders, hosts, and drives does not exceed
these limits, the 400 ns electrical cable length requirement will be met.
200 ns:
Phase change
delay to the host 200 ns:
Host delay to stop
free-running ACKS 200 ns:
Delay until the last ACK
arrives at the LSI53C320
800 ns from the phase change to the first REQ of the new phase
600 ns: Requirement for expander
Table 2.2 Total Cable Length for Ultra320 SCSI Using the LSI53C320
Number of Cascaded
Expanders
Maximum Physical Cable
Length in Meters (m) Comments
1 37
LSI Logic recommends limiting the 25 m
point-to-point bus cable length to 20 m and
the fully-loaded bus cable length to 12 m.
2 29
3 25
4 21