Spartan-3E FPGA Family: DC and Switching Characteristics
DS312 (v4.1) July 19, 2013
Product Specification
132
Timing Measurement Methodology
When measuring timing parameters at the programmable
I/Os, different signal standards call for different test
conditions.
Table 95 lists the conditions to use for each
standard.
The method for measuring Input timing is as follows: A
signal that swings between a Low logic level of VL and a
High logic level of VH is applied to the Input under test.
Some standards also require the application of a bias
voltage to the VREF pins of a given bank to properly set the
input-switching threshold. The measurement point of the
Input signal (VM) is commonly located halfway between VL
and VH.
The Output test setup is shown in
Figure 72. A termination
voltage VT is applied to the termination resistor RT, the other
end of which is connected to the Output. For each standard,
RT and VT generally take on the standard values
recommended for minimizing signal reflections. If the
standard does not ordinarily use terminations (e.g.,
LVCMOS, LVTTL), then RT is set to 1MΩ to indicate an open
connection, and VT is set to zero. The same measurement
point (VM) that was used at the Input is also used at the
Output.
X-Ref Target - Figure 72
Figure 72: Output Test Setup
FPGA Output
VT (VREF)
RT (RREF)
VM (VMEAS)
CL (CREF)
ds312-3_04_090105
Notes:
1.
The names shown in parentheses are
used in the IBIS file.
Table 95: Test Methods for Timing Measurement at I/Os
Signal Standard
(IOSTANDARD)
Inputs
Outputs
Inputs and
Outputs
VREF (V)
VL (V)
VH (V)
RT (Ω)VT (V)
VM (V)
Single-Ended
LVTTL
-
03.3
1M
01.4
LVCMOS33
-
0
3.3
1M
0
1.65
LVCMOS25
-
0
2.5
1M
0
1.25
LVCMOS18
-
0
1.8
1M
0
0.9
LVCMOS15
-
1.5
1M
0
0.75
LVCMOS12
-
0
1.2
1M
0
0.6
PCI33_3
Rising
-
25
0
0.94
Falling
25
3.3
2.03
PCI66_3
Rising
-
25
0
0.94
Falling
25
3.3
2.03
HSTL_I_18
0.9
VREF – 0.5
VREF + 0.5
50
0.9
VREF
HSTL_III_18
1.1
VREF – 0.5
VREF + 0.5
50
1.8
VREF
SSTL18_I
0.9
VREF – 0.5
VREF + 0.5
50
0.9
VREF
SSTL2_I
1.25
VREF – 0.75
VREF + 0.75
50
1.25
VREF
Differential
LVDS_25
-
VICM – 0.125
VICM + 0.125
50
1.2
VICM
BLVDS_25
-
VICM – 0.125
VICM + 0.125
1M
0
VICM
MINI_LVDS_25
-
VICM – 0.125
VICM + 0.125
50
1.2
VICM
LVPECL_25
-
VICM – 0.3
VICM + 0.3
1M
0
VICM
RSDS_25
-
VICM – 0.1
VICM + 0.1
50
1.2
VICM