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AP2500 Hardware Reference Guide 27
II. Components
II. System Components
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 device, additional devices are connected with cables to form a
“chain.” Terminating 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 termina-
tor 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.