Voltage levels for various bus standards

Signal type	Standard	VCC	VOH	VIH	Vt	VIL	VOL
Single Ended	5V CMOS	4.5-5.5	VCC-0.2	0.7 VCC	2.5	0.3 VCC	0.5
	2.5V CMOS	2.3-2.7	VCC-0.2	0.7 VCC	1.25	0.2 VCC	0.2
	3.3V CMOS LVTTL	3.0-3.6	2.4	2.0	1.5	0.8	0.4
	5V TTL	4.5-5.5	2.4	2.0	1.5	0.8	0.4
	ETL	4.5-5.5	2.4	1.6	1.5	1.4	0.6
	GTL		1.2	0.85	0.8	0.75	0.4
	GTLP		1.5	1.05	1	0.95	0.55
	TIA/EIA-232-F RS-232		5	3	0	-3	-5
Differential	Standard	VDD	VOH	VIH	Vdiff	VIL	VOL
	SSTL_3 Class I	3.3	2.1	1.9	0.4	1.1	0.9
	SSTL-3 Class II	3.3	2.3	1.9	0.4	1.1	0.7
	SSTL_2 Class I	2.5	1.82	1.7	0.35	0.8	0.68
	SSTL_2 Class II	2.5	2.01	1.7	0.35	0.8	0.49
	USB	4.5-5.5 3.0-3.6		2.0	0.2	1.3
	T1A/E1A -644 RS-644 LVDS	2.4	1.32	1.25	Vt=1.2	1.15	1.07