Product manual

2.6 Interface cable requirements
A characteristic impedance of 100 ohms + 10% is recommended for the
unshielded flat or twisted-pair interface cable. However, most available
cables have a somewhat lower characteristic impedance. To minimize
discontinuities and signal reflections, do not use cables of different
impedances on the same bus. If shielded and unshielded cables are
mixed within the same bus, the effect of impedance mismatch must be
carefully considered. This is especially important for maintaining ade-
quate margins for UltraSCSI transfer rates. UltraSCSI implementation
may require adjustments to cable length, the number of loads and the
transfer rates to achieve satisfactory system operation.
Part Manufacturer
Flat Cable 3M-3365-50
Twisted Pair Spectra Twist-N-Flat 455-248-50
2.6.1 Interface cable length for asynchronous
operation
The SCSI interface cable must meet the following requirements for
normal operation:
• The cable length cannot be longer than 6.0 meters.
• Cable stubs cannot be more than 0.1 meter long and must be
separated by at least 0.3 meter.
2.6.2 Interface cable for Fast SCSI operation
When using Fast SCSI synchronous data-transfer rates, the SCSI inter-
face cable must meet the following additional requirements:
• The cable length cannot be longer than 3.0 meters.
• The cable should not attenuate a 5-MHz signal more than 0.095 dB
per meter.
• The DC resistance at 20°C must not exceed 0.230 ohms per meter.
• A shielded, twisted-pair cable should not have a propagation delay
delta greater than 20 nsec per meter.
2.6.3 Interface cable for UltraSCSI operation
• The cable cannot be longer than 3.0 meters when using up to 4
devices.
Medalist Pro 2160N/2160WC Product Manual, Rev. A 25