Avago Technologies LSI53C895A - Manual (Page 64)

2-38 Functional Description
2.2.13.3 SCSI Termination
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 the
termination.
SE cables can use a 220
Ω
pull-up resistor to the terminator power
supply (Term Power) line and a 330
Ω
pull-down resistor to ground.
Because of the high-performance nature of the LSI53C895A, regulated
(or active) termination is recommended.
Figure 2.6 shows a Unitrode
active terminator. TolerANT technology active negation can be used with
either termination network.
For information on terminators that support LVD, refer to the SPI-3 draft
standard.
Note: If the LSI53C895A is to be used in a design that has only
an 8-bit SCSI bus, all 16 data lines must still be terminated.