User`s guide

MegaRUM II PCI Motherboard User’s Guide
34
Step 10 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