Virtex™-E 1.8 V Field Programmable Gate Arrays
R
DS022-3 (v2.6) November 9, 2001 www.xilinx.com Module 3 of 4
Preliminary Product Specification 1-800-255-7778 11
Calculation of Tioop as a Function of Capacitance
Tioop is the propagation delay from the O Input of the IOB to
the pad. The values for Tioop are based on the standard
capacitive load (Csl) for each I/O standard as listed in
Table 3.
For other capacitive loads, use the formulas below to calcu-
late the corresponding Tioop:
Tioop = Tioop + Topadjust + (Cload – Csl) * fl
where:
Topadjust is reported above in the Output Delay
Adjustment section.
Cload is the capacitive load for the design.
Table 3: Constants for Use in Calculation of Tioop
Standard Csl (pF) fl (ns/pF)
LVTTL Fast Slew Rate, 2mA drive 35 0.41
LVTTL Fast Slew Rate, 4mA drive 35 0.20
LVTTL Fast Slew Rate, 6mA drive 35 0.13
LVTTL Fast Slew Rate, 8mA drive 35 0.079
LVTTL Fast Slew Rate, 12mA drive 35 0.044
LVTTL Fast Slew Rate, 16mA drive 35 0.043
LVTTL Fast Slew Rate, 24mA drive 35 0.033
LVTTL Slow Slew Rate, 2mA drive 35 0.41
LVTTL Slow Slew Rate, 4mA drive 35 0.20
LVTTL Slow Slew Rate, 6mA drive 35 0.10
LVTTL Slow Slew Rate, 8mA drive 35 0.086
LVTTL Slow Slew Rate, 12mA drive 35 0.058
LVTTL Slow Slew Rate, 16mA drive 35 0.050
LVTTL Slow Slew Rate, 24mA drive 35 0.048
LVCMOS2 35 0.041
LVCMOS18 35 0.050
PCI 33 MHZ 3.3 V 10 0.050
PCI 66 MHz 3.3 V 10 0.033
GTL 0 0.014
GTL+ 0 0.017
HSTL Class I 20 0.022
HSTL Class III 20 0.016
HSTL Class IV 20 0.014
SSTL2 Class I 30 0.028
SSTL2 Class II 30 0.016
SSTL3 Class I 30 0.029
SSTL3 Class II 30 0.016
CTT 20 0.035
AGP 10 0.037
Notes:
1. I/O parameter measurements are made with the capacitance
values shown above. See the Application Examples
(Module 2) for appropriate terminations.
2. I/O standard measurements are reflected in the IBIS model
information except where the IBIS format precludes it.
Table 4: Delay Measurement Methodology
Standard VL1VH1
Meas.
Point
VREF
(Typ)2
LVTTL 0 3 1 .4 -
LVCMOS202.51.125-
PCI33_3 Per PCI Spec -
PCI66_3 Per PCI Spec -
GTL VREF –0.2 VREF +0.2 VREF 0.80
GTL+ VREF –0.2 VREF +0.2 VREF 1.0
HSTL Class I VREF –0.5 VREF +0.5 VREF 0.75
HSTL Class III VREF –0.5 VREF +0.5 VREF 0.90
HSTL Class IV VREF –0.5 VREF +0.5 VREF 0.90
SSTL3 I & II VREF –1.0 VREF +1.0 VREF 1.5
SSTL2 I & II VREF –0.75 VREF +0.75 VREF 1.25
CTT VREF –0.2 VREF +0.2 VREF 1.5
AGP VREF –
(0.2xVCCO)
VREF +
(0.2xVCCO)
VREF Per
AGP
Spec
LVDS 1 .2 –0.125 1.2 + 0.125 1.2
LVPECL 1.6 –0.3 1.6 + 0.3 1.6
Notes:
1. Input waveform switches between VLand VH.
2. Measurements are made at VREF (Typ), Maximum, and
Minimum. Worst-case values are reported.
I/O parameter measurements are made with the
capacitance values shown in Table 14. See the Application
Examples (Module 2) for appropriate terminations.
I/O standard measurements are reflected in the IBIS model
information except where the IBIS format precludes it.