Table of Contents
Advertisement
Setting SCSI Addresses
Each SCSI device requires a different SCSI address. The address is a number from 6 through 0 for 8-bit
devices, or from 6 through 0 and 15 through 8 for 16-bit devices. If two SCSI devices have the same
address, your system will not function correctly. SCSI address 7 is usually assigned to the adapter, so
additional SCSI devices can be set to addresses 6 through 0 and 15 through 8.
Determining Current SCSI Addresses
Manufacturers use many different methods to set SCSI addresses, including jumpers, dual inline package
(DIP) switches, push buttons, or dials. If your SCSI device is new, check the documentation that was
provided with the device to see if it specifies a default SCSI address. If a default address is not specified,
check how SCSI devices are set, then check the device itself for the current SCSI address. Be sure to
maintain a list of all your SCSI addresses for future reference (your system unit documentation may
provide a table where you can record them).
Planning SCSI Addresses
No two SCSI devices (on the same SCSI bus channel) should have the same SCSI address. Address 7 is
usually assigned to the adapter (address 6 is usually assigned to a second adapter).
Subsystems typically have fixed SCSI IDs that are preassigned to each drive slot on the bus. The
subsystems might also split the buses. For details, see your subsystem documentation.
In subsystems that have drives shared between two systems, each port of the subsystem is connected to
a different SCSI adapter. The second adapter's SCSI address must not conflict with that of any other
device. SCSI address 6 is often used for the second adapter. It may be necessary to remove a drive to
provide an address for the second adapter.
Note: System or subsystem backplane services may require an address of their own. This address is
usually ID 15.
Changing SCSI Addresses
To change SCSI addresses, follow the instructions in the documentation provided with each device.
Terminating the SCSI Devices and Adapter
Some SCSI devices have built-in terminators controlled by a DIP switch, jumper, or push button. Other
devices use terminators on the cable. Some devices require a terminator be plugged into the device on a
connector. After planning your installation, supply the correct terminator to the SCSI device on the device
end of the chain. The adapter always terminates at one end of the chain. Refer to the device instructions
to determine how it is terminated. If necessary, purchase terminators when you buy devices and cables.
For reliable SCSI operation, active terminators are required for all installations.
The basic rules of terminating SCSI buses are as follows:
v Terminate the ends of the chain.
v Do not terminate devices in the middle of the chain.
35
Appendix C. Connecting SCSI Devices to the Adapter
Advertisement
Table of Contents
