Maxtor ATLAS 10K III Manual download pdf (Page 331)

Appendix B. SCSI Bus Signal Timing

B–10 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives

B.3.2 SCSI ID Bits & Priorities

The SCSI standard permits a maximum of eight SCSI devices on a narrow (8 address

bits) SCSI bus and up to 16 devices on a wide (16 address bits) bus. Each SCSI

device has a single, unique SCSI ID address bit assigned to it. This SCSI ID

identifies and also sets the priority of the device on the bus. The bit priority is used

for arbitration as well as the SCSI ID.

See Table B–6 for the SCSI ID data bus bit assignments and the respective bit

priorities. Note that bit DB(7) has the highest priority for either 8-bit or wide (16-

bit) transfer modes. On the drive, the SCSI ID is assigned by configuring jumpers or

remote switches to the option connector in normal 3-bit (or 4-bit) binary fashion.

Chapter 2 has full instructions on setting the SCSI ID jumpers.

Since the drives are SCAM-1 compliant, a SCAM initiator may assign a SCAM SCSI

ID that is different than the one set with jumpers or switches.

Table B–6 SCSI ID Bits & Arbitration Priorities

DATA BUS

SCSI ID & PRIORITY

(8-BIT TRANSFERS)

SCSI ID & PRIORITY

(16-BIT TRANSFERS)

BIT NUMBER

ID (ADDRESS) PRIORITY

DB(7) 7 1 7 1

DB(6) 6 2 6 2

DB(5) 5 3 5 3

DB(4) 4 4 4 4

DB(3) 3 5 3 5

DB(2) 2 6 2 6

DB(1) 1 7 1 7

DB(0) 0 8 0 8

DB(15) – − 15 9

DB(14) – − 14 10

DB(13) – − 13 11

DB(12) – − 12 12

DB(11) – − 11 13

DB(10) – − 10 14

DB(9) – − 9 15

DB(8) – − 8 16

NOTE: A single bit is used to identify a device and define its priority on the SCSI bus. Highest

priority (1) is at the top.

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Maxtor ATLAS 10K III Manual Page 331