USPIIe-USB Hardware Manual
1-6
Themis Computer
Figure 1-2.
SCSI Termination Configurations
Terminator
Terminator
SCSI B Bus
SCSI A Bus
Terminator
Terminator
P1 Connector
Front Panel
State = On
State = On/Off
*
SCSI Controller
Last
SCSI A
Device
Logic**
Sensing Line
Sensing Line
Last
SCSI A
Device
P2 Connector
Terminator
Last
SCSI B
Device
0/1
0/1
+
+
**
Logic Table
P2
Bus
Front
Panel
Disable (Off)
Enable (On)
Enable (On)
Disable (Off)
Termination ON
1
1
0
0
0
0
1
1
Paddle
Board
*
On-board terminator automatically
turns
when there is no device
attached to the P2 connector, and
when a device is attached to
the P2 connector.
on
off
Termination OFF
Termination ON
Termination OFF
Note:
The SCSI-A channel actually has two terminating circuits. One is associ-
ated with the front-panel SCSI-A connection, which automatically turns itself off
whenever a SCSI device is attached to the front panel. The other is associated with
the VME P2 SCSI-A connection, which also automatically turns itself off when-
ever a SCSI device is attached to the P2 connector.
This design allows for proper SCSI-A bus termination for any combination of de-
vices that may be attached (e.g., no devices at either end of the SCSI-A bus, a de-
vice on one end but not the other, or a device on each end).
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