Seagate ST373455LW, ST3146855LC manual LVD Input characteristics, General cable characteristics

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 = < Vin = < 3.6 V (signal negation/logic 0) Steady state High level input differential voltage = –3.6 V = < Vin = < –0.030 V (signal assertion/logic 1) Differential voltage = +0.030 V minimum with common-mode voltage range 0.845 V = < Vcm = < 1.685 V. (T10/1302D revision 20b, section A.3.1).

	VCCA		VCCB
Single	LVD Signal Drivers	Single	Single
Ended		Ended	Ended
Circuitry		Receiver	Negation
	LVD		Driver
	Receiver
Single			Single
Ended			Ended
Ground			Assertion
Driver			Driver
	LVD Signal Drivers
Ground

Single Ended:	GND	—Signal
LVD:	+Signal	—Signal

Figure 18. Typical SE-LVD alternative transmitter receiver circuits

10.7.1.1General 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.

10.7.1.2Single-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 21 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 21: Cable characteristics for single-ended circuits

		Maximum length	Transmission line impedance
	Maximum number of	between SCSI S.E.
I/O transfer rate	devices on the bus	terminators	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

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.

Cheetah 15K.5 SCSI Product Manual, Rev. J 69