Avago Technologies LSI8751D - Manual (Page 47)

PCI Cache Mode 2-23
2.5.9.2 Terminator Networks
The terminator networks provide the biasing needed to pull signals to an
inactive voltage level, and to match the impedance seen at the end of
the cable with the characteristic impedance of the cable. Terminators
must be installed at the extreme ends of the SCSI chain, and only at the
ends. No system should ever have more or less than two terminators
installed and active. SCSI host adapters should provide a means of
accommodating terminators. There should be a means of disabling
termination.
SE cables can use a 220
Ω
pull-up to the terminator power supply
(Term Power) line and a 330
Ω
pull-down to ground. Because of the
high-performance nature of the LSI53C875, regulated (or active)
termination is recommended.
Figure 2.4 shows a Unitrode active
terminator. For additional information, refer to the SCSI-2 Specification.
TolerANT technology active negation can be used with either termination
network.
Note: If the LSI53C875 is to be used in a design with only an
8-bit SCSI bus, all 16 data lines still must be terminated or
pulled high. Active termination is required for Ultra SCSI
synchronous transfers.