
XA Spartan-3A DSP Automotive FPGA Family Data Sheet
DS705 (v2.0) April 18, 2011
Product Specification
29
Timing Measurement Methodology
When measuring timing parameters at the programmable I/Os, different signal standards call for different test conditions.
Table 27 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 9. 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 (for example, LVCMOS, LVTTL), then RT
is set to 1 M
to indicate an open connection, and V
T 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 9
Figure 9: Output Test Setup
Table 27: Test Methods for Timing Measurement at I/Os
Signal Standard
(IOSTANDARD)
Inputs
Outputs
Inputs and
Outputs
VREF (V)
VL (V)
VH (V)
RT ()VT (V)
VM (V)
Single-Ended
LVTTL
–
0
3.3
1M
0
1.4
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
–
0
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
HSTL_I
0.75
VREF – 0.5
VREF + 0.5
50
0.75
VREF
HSTL_III
0.9
VREF – 0.5
VREF + 0.5
50
1.5
VREF
HSTL_I_18
0.9
VREF – 0.5
VREF + 0.5
50
0.9
VREF
HSTL_II_18
0.9
VREF – 0.5
VREF + 0.5
25
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
SSTL18_II
0.9
VREF – 0.5
VREF + 0.5
25
0.9
VREF
SSTL2_I
1.25
VREF – 0.75
VREF + 0.75
50
1.25
VREF
FPGA Output
VT (VREF)
RT (RREF)
VM (VMEAS)
CL (CREF)
DS705_09_041311
Notes:
1.
The names shown in parentheses are
used in the IBIS file.