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CHAPTER 3: Configuration and Internal LEDs
3.1 Configuring Termination
Both ends of any SCSI-bus segment attached to the Expander need to be
terminated in order to prevent electronic “echo” interference on the bus that
would degrade its performance. You can use the Expander’s internal jumpers JP1,
JP4, and JP5 to control this termination. JP1 and the lower posts of JP5 affect the bus
attached to the HVD port , while JP4 and the upper posts of JP5 affect the bus
attached to the LVD/SE port.
•Termination at the Expander (JP5): How you should set jumpers on the four
posts at JP5, which control local termination at the Expander’s ports, depends
on how your cables will be attached to the Expander. Just remember that the
upper and lower JP5 posts have opposite values: For the lower (HVD) posts, OFF
(empty) is terminated and ON (installed) is unterminated; for the upper
(LVD/SE) posts, ON is terminated and OFF is unterminated.
– For each port into which you will be directly plugging a single cable, so that
the SCSI-bus segment will start or end at that port, leave the jumper positions
just as they come from the factory. If a segment will start or end at the HVD
port, leave the jumper OFF the lower posts. If a segment will start or end at
the LVD/SE port, leave the jumper ON the upper posts.
Example: For simple conversion applications in which an LVD bus ends at
the Expander and an HVD bus starts, or vice versa, leave the jumpers
installed on upper JP5 and leave lower JP5 empty.
– For each port into which you will be plugging two cables through a three-
connector adapter (not a stub cable!), so that the SCSI-bus segment will pass
through that port, remove the jumper. If a segment will pass through the
HVD port, install a jumper on the lower posts. If a segment will pass through
the LVD/SE port, remove the jumper from the upper posts.
Example: For applications in which you are allowing a segment of HVD
devices to tap into an LVD bus without forcing the LVD bus to operate at
the data rate of the HVD segment, remove the jumper from upper JP5. If
the HVD segment ends at the Expander, leave the lower JP5 jumper posts
empty. But if the HVD segment also passes through the Expander, install a
jumper on the lower JP5 posts.
Refer to Figures 3-1 through 3-3 on the next page. In an application such as
that shown in Figure 3-1, lower JP5 should remain empty and upper JP5 should
remain installed. In an application like that in Figure 3-2, with the Expander in
the middle of one segment and at the end of another, set the jumper oppositely
for the port that’s attached to the middle of the segment. In a wide-open
application like that in Figure 3-3, in which the Expander is in the middle of
both segments, remove the jumper from upper JP5 and install it on lower JP5.