Quantum 10K II User Manual
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
1
ID (ADDRESS)
PRIORITY
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
1
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.