Logic PCI to Dual Channel SCSI Host Adapter User's Guide LSI21003

2-16 Installing the LSI21003
bus and its termination is automatically enabled when it is connected to
the end of the bus.
Important: To utilize Ultra160 SCSI performance, you must only have
LVD devices on the bus. Do not mix any SE devices with
LVD devices or the entire bus will drop to SE, limiting bus
performance to Ultra SCSI levels.
LVD peripheral devices are normally terminated with external
terminators, but are sometimes set with jumpers or with a switch on the
peripheral. Refer to the peripheral manufacturer’s instructions and to the
computer’s user’s manual for information on how to identify the
terminator setting of each device and how to change it.
Caution:
The autoenable/disable sensing feature on your LSI21003
may enable termination erroneously if it is directly cabled to
another SCSI device or host adapter using the same
sensing method. The LSI21003 senses SCSI devices by
detecting the ground signal on conductor 22 of a
50-conductor internal cable, conductor 36 of a
50-conductor external cable, or conductor 50 of a
68-conductor cable.
The LSI21003 automatically controls SCSI bus termination for four
different bus configurations. The four bus configurations are:
• Connections for high density internal SCSI connections
• Connections to high and low density internal connectors
• Connections for external SCSI connection
• Connections to both internal and external SCSI connectors
These terminations are discussed below. Please note that only SE
termination control is allowed on Channel A.
2.2.4.1 High Density Internal SCSI Connections
If only internal SCSI device connections on the host adapter have been
made, then terminate the last internal device on the SCSI bus. You must
disable the termination on all other devices. Termination on the LSI21003
is automatically enabled for Channel A. The termination for Channel B is
enabled all the time.