Seagate ST373454 Manual download pdf (Page 78)

68 Cheetah 15K.3 SCSI Product Manual, Rev. G

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

= < 3.6 V (signal negation/logic 0)

Steady state High level input differential voltage = –3.6 V = < V

= < –0.030 V (signal assertion/logic 1)

Differential voltage = +

0.030 V minimum with common-mode voltage range 0.845 V = < V

= < 1.685 V.

(T10/1302D revision 20b, section A.3.1).

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 19 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.

Single-ended I/O cable pin assignments for LW drives are shown in Table 16.

Single-ended I/O pin assignments for LC models are shown in Table 17. The LC model does not require an I/O

cable. It is designed to connect directly to a back panel connector.

Table 19: 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

Receiver

Ground

GND

+Signal

—Signal

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