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22 AP100 Hardware Reference Guide
II. System Components
II. Components
SCSI Information
SCSI Information
SCSI Connections
Your server can support up to 15 user installed single-ended SCSI devices.
Be sure to include both internal and external SCSI devices in your device
setup. Each SCSI device (both internal and external) must have a unique
address (or SCSI ID). Check your SCSI device documentation for instruc-
tions. Be sure to record all SCSI addresses so that you can prevent SCSI
address conflicts.
SCSI Termination
SCSI devices are connected together in a “chain” by cables. Internal de-
vices connect to the motherboard with a 50 pin or 68 pin flat ribbon cable.
External SCSI devices may be connected using an external SCSI connector
or SCSI card with an external connector. If there are more than one internal
or external devices, additional devices are connected with cables to form a
“daisy chain.” Terminating the devices on the ends of the SCSI Bus “chain”
is necessary for SCSI devices to work properly. SCSI devices normally come
with its termination enabled by jumpers or dip switches. You must disable
these termination for devices in between the SCSI chain. Ultra2 devices do
not have a termination jumper and must be terminated using a terminator on
the SCSI cable. The terminator must always be on the end of the cable
which means that you cannot connect a device on the last connector.
SCSI ID Jumpers
All SCSI devices, including this motherboard with onboard SCSI, must have a SCSI
identification number that is not in use by any other SCSI device. There are sixteen
possible ID numbers, 0 through 15. The SCSI ID serves two purposes:
• It uniquely defines each SCSI device on the bus.
• It determines which device controls the bus when two or more devices try to use
it at the same time.
SCSI IDs on one channel do not interfere with the IDs on another channel. You can
connect up to 15 SCSI devices to this motherboard. You must set a SCSI ID number
(ID 0 to ID 15) for each device. Note that the onboard SCSI chipset is also a SCSI
device and will also require a SCSI ID number. SCSI devices vary in how they set the
ID number. Some use jumpers, others have some kind of selector switch. Refer to the
manual for any device you install for details on how to set its ID number.
SCSI ID Priority
The motherboard has an onboard 16bit single-channel SCSI chipset. SCSI ID 15
has the highest priority, and SCSI ID 0 has the lowest priority.