Termination/Term Power - HP 9000 Series Service Manual

SCSI Peripherals and I/O Information
Signal Name
+MSG 25
+SEL 26
+C/D 27
+REQ 28
+I/O 29
Ground 30
+DB(8) 31
+DB(9) 32
+DB(10) 33
+DB(11) 34

Termination/Term Power

1. The SCSI bus requires termination at both ends of the bus. The host adapters generally supply on
board terminators and should be located at one end of the bus. The multifunction I/O host bus
adapters are the current exception since they are designed to reside in the middle of the SCSI bus.
Therefore, buses associated to these multifunction I/O adapters are terminated on the two ends of
the associated internal and external buses. Since an external connection may not be present, insure
that the ACTIVE terminators supplied with the product are installed on the external connection at
the back of the system.
2. When possible, put devices that supply termination power at both ends of the bus. The host
adapters will always supply termination power which is required for proper bus operation.
However, noise immunity can be improved by placing another source of termination power at the
other end of the bus. Most peripheral devices are optionally capable of supply termination power.
(See the appropriate peripheral descriptions in this section.)
Termination Characteristics and Power
Terminator power - Will be supplied by the Initiators and may be supplied by any or all connected
devices. HP recommends that terminator power be supplied by the Host Bus Adapter (HBA) Initiator
and the last device on the SCSI Bus to help decrease interface error rates and provide better balance to
the TERMPWR contacts. Recommended current limiting is 1.5 amps. with a maximum of 5 amps.
(The limiting device may be fused or resetable.)
Single-Ended
TERMPWR = 4.25 to 5.25 vdc. with 900 ma source drive capability for the 50-pin Cable, and 1500
ma source drive capability for the 68-pin cable.
11-8
Connector Cable
Contact Conductor
Number Number
49
51
53
55
57
59
61
63
65
67
Cable Connector
Conductor Contact
Number Number
50 59
52 60
54 61
56 62
58 63
60 64
62 65
64 66
66 67
68 68
Signal Name
-MSG
-SEL
-C/D
-REQ
-I/O
Ground
-DB(8)
-DB(9)
-DB(10)
-DB(11)
Chapter 11