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66
+5V
5.6K
TE
Transmit/Receive
Enable
[1]
RE
DIFFSENS [6]
Disable
Transmit or
Receive
R
Signal [2]
SCSI Device at Beginning of I/O Cable
(usually Host Adaptor/Initiator)
Notes.
[1]
Positive logic enables transmitter (+5 V = asserted)
Negative logic enables receivers (0 V = asserted)
[2]
Negative logic signal (0 V = asserted)
[3]
Total interface cable length should not exceed value given in Section 9.6.3.2 from first SCSI device at
beginning to end of daisy chain. See Section 9.7.2 for signal characteristics.
[4]
I/O line terminators. If SCSI device is a Seagate disc drive, terminators and a place to plug them in must
be provided external to the drive by user, systems integrator or host equipment manufacturer where
needed. The drive has no terminators and there are no provisions on the drive for terminator installation.
[5]
Arrangements for connecting terminator power to the terminators must be made by the systems designer.
As a help, drive +5 V power is made available on SCSI bus ("N," "W," and "WD" models) for powering
external terminators if the drive option select header jumper TP (Figure 10) is installed in rightmost posi-
tion "TP." See pin assignment Tables 13b and 13c for pins assigned to terminator power.
[6]
SCSI I/O line (pin 21) disables I/O circuits if single-ended cable plugged in or cable plugged in upside
down.
[7]
SCSI I/O cable ground. See Table 13b and Table 13e.
Figure 21.
Typical differential I/O line transmitter/receiver and external terminators
+5V
Term
Power
LSI
XCVR
1
1
2
+5V
5.6K
Transmit/Receive
Enable
DIFFSENS [6]
Transmit or
Receive
Signal [2]
SCSI Device at End of I/O Cable
(Drive/Target)
Cheetah 4LP Product Manual, Rev. B
[5]
330
[4]
Ohm
150
Ohm
330
Ohm
[7]
+5V
TE
LSI
XCVR
[1]
RE
Disable
1
1
R
2
[3]
Twisted or Flat
Cable Pair
Term
[5]
Power
330
[4]
Ohm
150
Ohm
330
Ohm
[7]
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