Digital Equipment VAXstation 3100 Maintenance Manual page 62

Troubleshooting 41
All of the expansion boxes connect to the SCSI
port
on the back of the system
box using a daisy-chain cabling scheme. A SCSI terminator must be installed
on the connector of the last expansion box or installed on the SCSI port
connector if no expansion boxes are used. The TKSOZ-FA expansion box
must be installed last on the daisy chain because it contains internal SCSI,
bus termination resistors and does not need the SCSI terminator connected to
it. However, the TKSOZ-GA exransion box (with the SCSI ID switch on the
back) does not have the interna resistors i,nstaJled. This expansion box must
have the SCSI terminator installed for the SCSI bus to operate properly.
Each device on the SCSI bus, including the SCSI bus controller, has its own
address ID location. The SCSI bus controller aJways bolds the address ID
of 6 for all buses. The address ID assignments for the devices differ slightly
between model 30 and model 40 as shown in Table 2-12 (model 30) and
Table
2-13 (model 40). Note that if two RRD40 devices are to be installed
(one internal and one externaJ), the internal RRD40 adapter board should be
set to address ID 4 and the external expansion box should be set to one of the
open address IDs.
Table 2-12 Model 30 SCSI Bus Address ID Assignments
SCSI-A Bus {SCSI/SCSI)
RZ22 or RZ23 disk drive (system disk)
TZ30 tape drive
SCSI bus controller
Reserved for expansion
SCSI-A Bus (ST506/SCSI) or SCSI-B (SCSI/SCSI)
RRD40 compact disc drive expansion box (external)
RZ22 or RZ23 disk drive (system disk)
RZ22 or RZ23 disk drive (user
disk)
RZ55 disk drive expansion box
RZ55 disk drive expansion box (second box)
SCSI bus controller
Internal TZ30 tape drive or TKSOZ expansion box
Reserved for expansion
Address ID
3
5
6
1
4
3
2
1
0
6
5
7