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7 Series FPGAs SelectIO Resources User Guide www.xilinx.com 51
UG471 (v1.5) May 15, 2015
Supported I/O Standards and Terminations
In Verilog, the Verilog constraint is placed immediately before the module or instantiation
of the IOB primitive. The Verilog constraint is specified as follows:
(* VCCAUX_IO = {NORMAL|HIGH|DONTCARE}*)
UCF and NCF Syntax
NET “net_name” VCCAUX_IO=(0|NORMAL|HIGH|DONTCARE);
INST “instance_name ” VCCAUX_IO=(NORMAL|HIGH|DONTCARE);
7 Series FPGA I/O Resource VHDL/Verilog Examples
The VHDL and Verilog example syntaxes for instantiating 7 series FPGA I/O resources are
found in UG768
: Xilinx 7 Series FPGA Libraries Guide for HDL Designs.
Supported I/O Standards and Terminations
The following sections provide an overview of the I/O standards and options supported
by all 7 series devices.
While most 7 series FPGA I/O supported standards specify a range of allowed voltages,
this chapter records typical voltage values only. Detailed information on each specification
can be found on the Electronic Industry Alliance JEDEC web site at http://www.jedec.org
.
LVTTL (Low Voltage TTL)
LVTTL is a general-purpose EIA/JESD standard for 3.3V applications that uses a
single-ended CMOS input buffer and a push-pull output buffer. This standard requires a
3.3V output source voltage (V
CCO
), but does not require the use of a reference voltage
(V
REF
) or a termination voltage (V
TT
). This standard is defined by JEDEC (JESD 8C.01).
Sample circuits illustrating both unidirectional and bidirectional LVTTL termination
techniques are shown in Figure 1-37 and Figure 1-38. These two diagrams show examples
of source-series and parallel terminated topologies.
Table 1-9: Available I/O Bank Type
HR HP
Available N/A
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