Seagate Ultra 160 Fast-160 Fast-320 Comments, Total transmitter error budget Receiver errors

Table 9: SCSI Fast-160 and fast 320 non-compensatable timing budget in nanoseconds

Item		Fast-160			Fast-320			Comments
REQ(ACK) period			12.5			6.25		From Table 7
Transfer period			6.25			3.125		REQ(ACK) period / 2
		Total		Post	Total		Post	Worst case total of + and - time
				Compen			Compen
Transmitter and receiver errors:		Errors		sation	Errors		sation	shift except where noted
Transmitter errors:
	REQ(ACK) period tolerance / 2	0.06		0.06	0.06		0.06	Tolerance of transmitter plus mea-
								surement error b
	Clock Jitter	0.25		0.25	0.25		0.50
	System noise at transmitter	0.25		0.25	0.2		0.2	Time impact
	Transmitter chip skew	0.75		0	0.75		0
	Transmitter trace skew	0.2		0	0.2		0
	Transmit time asymmetry	0.50		0.50	0.50		0	Compensated for on fast-320
								SCSI devices
Total transmitter error budget:		2.01		1.06	1.96		0.51
Receiver errors:
	System noise at receiver	0.25		0.25	0.2		0.2	Time impact
	Chip noise in receiver	0.2		0.2	0.2		0.2	Time impact
	Receiver chip skew	0.75		0	0.75		0
	Receiver trace skew	0.2		0	0.2		0
	Receiver time asymmetry	0.35	0.35		0.35	0
	Residual skew error	0		0.3	0		0.2	After skew compensation
	Strobe offset tolerance	0		0.5	0		0.2	Accuracy of centering strobe
	Offset induced time asymmetry	N/A a		N/A a	0.8		0.2	Time impact from cumulative D.C.
								offsets at receiver
	Receiver amplitude time skew	0.2		0.2	0.2		0.05
Total receiver error budget:		1.95		1.8	2.7		1.05
Total Transmitter + receiver error		3.96		2.86	4.44		1.53
budget:
Total timing error budget for		2.29		3.39	-1.535		1.565	Transfer period - (total transmitter
								+ total receiver error budget)
interconnect and system margin:

aTiming budgets in some previous standards neglected asymmetry & detection ambiguity and lumps chip noise, clock jitter, crosstalk time shift, noise, ISI and receiver amplitude skew into other terms (e.g., signal distortion skew) and/or ignores the effects.

bTolerance adjusted for half cycle (i.e., transfer period)

Parallel SCSI Interface Product Manual, Rev. A ) 25