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Cheetah 10K.7 SCSI Product Manual, Rev. D 81
LVD input characteristics
Each differential signal received by LVD interface receiver circuits shall have the following input characteristics
when measured at the disc drive connector:
Steady state Low level input differential voltage = 0.030 V = < V
in
= < 3.6 V (signal negation/logic 0)
Steady state High level input differential voltage = –3.6 V = < V
in
= < –0.030 V (signal assertion/logic 1)
Differential voltage = +
0.030 V minimum with common-mode voltage range 0.845 V = < V
cm
= < 1.655 V.
(T10/1302D revision 14, section A.3.2).
Figure 27. Typical SE-LVD alternative transmitter receiver circuits
9.7.1.1 General cable characteristics
To minimize discontinuities and signal reflections, cables of different impedances should not be used in the
same bus. Implementations may require trade-offs in shielding effectiveness, cable length, the number of
loads, transfer rates, and cost to achieve satisfactory system operation. If shielded and unshielded cables are
mixed within the same SCSI bus, the effect of impedance mismatch must be carefully considered. Proper
impedance matching is especially important in order to maintain adequate margin at fast SCSI transfer rates.
9.7.1.2 Single-ended drivers/receivers
The maximum total cable length allowed with drives using single-ended I/O driver and receiver circuits
depends on several factors. Table 18 lists the maximum lengths allowed for different configurations of drive
usage. These values are from the SPI documents. All device I/O lines must have equal to or less than 25 pf
capacitance to ground, measured at the beginning of the stub.
A stub length of no more than 0.1 meter (0.33 ft) is allowed off the mainline interconnection with any connected
equipment. The stub length is measured from the transceiver to the connection to the mainline SCSI bus.
Table 18: Cable characteristics for single-ended circuits
I/O transfer rate
Maximum number of
devices on the bus
maximum length
between SCSI S.E.
terminators
Transmission line impedance
REQ/ACK Other signals
<
10M transfers/s (Fast 10) 16 (wide SCSI bus) 3 meters (9.8 ft) 90 + 6 Ohms 90 + 10 Ohms
<
20M transfers/s (Fast 20) 4 (wide SCSI bus) 3 meters (9.8 ft) 90 + 6 Ohms 90 + 10 Ohms
<
20M transfers/s (Fast 20) 8 (wide SCSI bus) 1.5 meters (4.9 ft) 90 + 6 Ohms 90 + 10 Ohms
VCCA VCCB
Single
Ended
Circuitry
Single
Ended
Receiver
Single
Ended
Negation
Driver
Single
Ended
Assertion
Driver
Single
Ended
Ground
Driver
Single Ended:
LVD:
LVD Signal Drivers
LVD Signal Drivers
LVD
Receiver
Ground
GND
+Signal
—Signal
—Signal