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MegaRUM PCI Motherboard User’s Guide38
Step 11 Connect SCSI I/O, Continued
Single-Ended Ultra SCSI Understanding the cable requirements, termination and stub lengths is
key to the successful implementation of a Ultra-SCSI subsystem.
SCSI Cables - Up to Four Devices The total external SCSI cable length for single-ended when
using up to 4 Ultra-SCSI devices (maximum. capacitance of device = 25pf)
should be less than or equal to:
(3 meter-(SCSI signal length on AMI RAID)-(SCSI length in storage box)
= (3 meter - 0.305 meter - SCSI length in storage box)
= 2.695 - SCSI length in storage box
SCSI Cables - More than Four Devices The total external SCSI cable length for single-ended
when using from five to eight Ultra-SCSI devices (max. cap of device = 25pf)
should be less than or equal to:
(1.5 meter-(SCSI signal length on AMI RAID)-(SCSI length in storage box)
= (1.5 meter - 0.305 meter - SCSI length in storage box)
= 1.195 - SCSI length in storage box
Spacing Devices The SCSI devices should be uniformly spaced between terminators with the
end devices located as close as possible to the terminators.
SCSI Signal Path The SCSI signal path is a controlled impedance environment with the
following characteristic impedance:
90 ohms +/- 6 ohms for the REQ and ACK signals
90 ohms +/- 10 ohms for all other signals
Cont’d