Figure 23. Typical Se-Lvd Alternative Transmitter Receiver Circuits - Seagate ST336732LC Product Manual

68
Steady state Low level input differential voltage = 0.030 V = < V
Steady state High level input differential voltage* = –3.6 V = < V
Differential voltage = +0.030 V minimum with common-mode voltage range 0.700 V = < V
(X3T10/1142D revision 20b Section A.3.1)
Figure 23. 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 tradeoffs 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 20 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.
Table 20: Cable characteristics for single-ended circuits
I/O transfer rate
<10M transfers/s (Fast-10)
<20M transfers/s (Fast-20)
<20M transfers/s (Fast -20)
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.
Single-ended I/O cable pin assignments for LW drives are shown in Table 17.
Single-ended I/O pin assignments for LC models are shown in Table 18. The LC model does not require an I/O
cable. It is designed to connect directly to a back panel connector.
9.7.1.3 Low voltage differential I/O circuits
The maximum SCSI bus length between the terminators for a SCSI LVD point-to-point system (one initiator
and one target) is 25 meters.
VCCA
LVD Signal Drivers
Single
Ended
Circuitry
Receiver
Single
Ended
Ground
Driver
LVD Signal Drivers
Ground
Single Ended: GND
LVD: +Signal
Maximum number of
devices on the bus
16 (wide SCSI bus)
4 (wide SCSI bus)
8 (wide SCSI bus)
Cheetah X15 36LP Product Manual, Rev. D
= < 3.6 V (signal negation/logic 0)
IN
= < –0.030 V (signal assertion/logic 1)
s
VCCB
Single
Ended
Receiver
LVD
—Signal
—Signal
Maximum length Transmission line impedance
betwen SCSI S.E.
terminators REQ/ACK
3 meters (9.8 ft) 90 + 6 Ohms
3 meters (9.8 ft) 90 + 6 Ohms
1.5 meters (4.9 ft) 90 + 6 Ohms
= < 1.800 V.
cm
Single
Ended
Negation
Driver
Single
Ended
Assertion
Driver
Other signals
90 + 10 Ohms
90 + 10 Ohms
90 + 10 Ohms