phase 5 CYBERSTORM MKIII, Руководство пользователя

Страница: 45 / 57

SCSI-BUS TERMINATION
To provide error-free operation of the SCSI bus system, it is absolutely necessary that the SCSI
bus is electrically terminated in a correct way. You can imagine the SCSI bus being a single cable
which must be actively terminated at each ends of the cable. The indicivdual SCSI devices are then
beeing connected to the cable directly between these terminated ends, and the SCSI controller its-
elf also acts as a SCSI device (please also see Figure 7).
In the real-world application this means that the first and the last SCSI device in the SCSI chain
must be actively terminated, and the connection to the controller must be made some–where bet-
ween the first and the last device. There is also one special case, which is the possible translation
from a WIDE SCSI bus (16 bit date) to a Fast SCSI bus (8 bit data). At this point, all data lines which
are only implemented on the WIDE SCSI bus (the upper 8 data lines) must be terminated active-
ly, while the lower 8 data lines must then be terminated at the end of the Fast SCSI bus. Therefo-
re it is necessary to use WIDE to Fast SCSI adaptors with the described integrated termination
when Fast SCSI devices shall be connected to the
CYBERSTORM MKIII SCSI controller.
The CYBERSTORM MKIII SCSI controller doesn't have an own active termination, as there are
too many possible custom configurations. The termination will be done either with SCSI devices at
the end of the chain, or – in case only one SCSI device is connected to the SCSI bus – with an
additional active terminator (see Figure 8).
Older SCSI devices such as hard disks, removable drives, or streamers mostly have passive ter-
minators installed. These terminators are usually located nearby the SCSI connector of the devi-
ce. These passive terminators can not be used on the SCSI bus of the CYBERSTORM MKIII SCSI
controller, and must always be removed as the SCSI bus must be actively terminated. If these pas-
sive termination resistors (usually resistor arrays) are not socketed, which is sometimes the case
with devices where the termination resistors are SMD soldered, they can usually be disabled by a
jumper or a switch on the SCSI devices. In any case, please refer to the manual or technical docu-
43
Figure 8.
A correct connected
Ultra-Wide-SCSI Harddrive
on the CYBERSTORM MKIII
Ultra-Wide-SCSI Controller
Active
Terminator
Active
Terminated
Ultra-WIDE-SCSI
Harddisk
Connector of the
Ultra-WIDE-SCSI Controller
on the CYBERSTORM