Seagate STD124000N Product Manual page 29

Installation
Product Manual
All signals except GROUND and TEMPWR must be terminated at both ends of the
cable. Each signal termination consists of 220 ohms (± 5%) to TEMPWR and 330
ohms (± 5%) to GROUND and must meet the following specifications or
requirements:
z
Terminators must supply a characteristic impedance of 100 to 132 ohms.
z
External terminators must be powered by the TEMPWR line, and units that
provide terminator power to the cable must have:
V = 4.25 to 5.25 VDC
TERM
900 milliamps minimum source drive capability
The external drive normally supplies terminator power to the SCSI bus.
z
When TEMPWR matches the above values, the voltage of released signal lines
must be at least 2.5 VDC.
z
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.
z
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 drive are:
z
Signal assertion (low-level output voltage): 0.0 to 0.5 VDC at 48 milliamps
sinking
z
Signal negation (high-level output voltage): 2.5 to 5.25 VDC
Signals received by the drive have the following characteristics.
z
Signal assertion (low-level input voltage): 0.0 to 0.8 VDC
z
Signal negation (high-level input voltage): 2.0 to 5.25 VDC
z
Maximum input load (low-level input current): –0.4 at 0.5 VDC
z
Minimum input hysteresis: 0.2 VDC
Chapter 3
Page 17