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INSTALLA TION
All signals except GROUND and TEMPWR must be terminated at both ends of the cable. Each signal
termination consists of 220 ohms (+ or -5%) to TEMPWR and 330 ohms (+ or -5%) to GROUND and must
meet the following specifications:
o
Terminators must supply a characteristic impedance of 100 to 132 ohms.
o
External terminators must be powered by the TEMPWR line, and units providing terminator power
to the cable must have:
V
TERM
= 4.25 to 5.25 VDC
900 milliamps minimum source drive capability
o
The external drive normally supplies terminator power to the SCSI bus.
o
When TEMPWR matches the above values, the voltage of released signal lines must be at least 2.5
VDC.
o
When a driver asserts a line and pulls it to 0.5 VDC, the current available to the signal line driver
may not exceed 48 milliamps. The first two terminators may only supply 44.8 milliamps of this
current.
o
When at least one device supplies TEMPWR, these conditions may be met by any valid
configuration of targets and initiators.
All signals use open-collector drivers. The output characteristics (measured at the connector of the drive) of
signals driven by the Python drive are:
o
Signal assertion (low-level output voltage): 0.0 to 0.5 VDC at 48 milliamps sinking
o
Signal negation (high-level output voltage): 2.5 to 5.25 VDC
Signals received by the Python drive have the following characteristics.
o
Signal assertion (low-level input voltage): 0.0 to 0.8 VDC
o
Signal negation (high-level input voltage): 2.0 to 5.25 VDC
o
Maximum input load (low-level input current: - 0.4 at 0.5 VDC
o
Minimum input hysteresis: 0.2 VDC
3.4.3 Single-Ended SCSI Connector - Internal Models 4322 and 4542
The Python 4322 and 4542 internal drives provide a 50-pin, right-angle, dual-row connector on the main
PCB at the rear of the drive. The pin assignments for this single-ended connector are listed in Table 3-1.
NOTE: All odd pins except pin 25 are connected to signal ground at the drive. Pin 25
is
left
open. A signal name or abbreviation preceded by a - (dash) indicates that the signal
is
active-low.
3-3
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