UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

Page Bookmarked

AR# 37171

7 Series, Virtex-6/-5/-4, Spartan-6 - How do you enable internal Differential Termination?

Description

How do you enable Differential Termination for true differential input IOSTANDARDs?

Solution

You can enable internal DIFF_TERM in the following ways:

Enable DIFF_TERM in HDL Code. 

The Language Templates and device Libraries Guide contain the instantiation template for the IBUFDS/IBUFGDS which contains an attribute DIFF_TERM that is set to TRUE to enable the DIFF_TERM.

Example VERILOG Instance:


IBUFDS #(
.DIFF_TERM("TRUE"), // Differential Termination
.IOSTANDARD("DEFAULT") // Specify the input I/O standard
) IBUFDS_inst (
.O(O), // Buffer output
.I(I), // Diff_p buffer input (connect directly to top-level port)
.IB(IB) // Diff_n buffer input (connect directly to top-level port)
);

Example VHDL:


IBUFDS_inst : IBUFDS
generic map (
DIFF_TERM => TRUE, -- Differential Termination
IBUF_LOW_PWR => TRUE, -- Low power (TRUE) vs. performance (FALSE) setting for referenced I/O standards
IOSTANDARD => "DEFAULT")
port map (
O => O, -- Buffer output
I => I, -- Diff_p buffer input (connect directly to top-level port)
IB => IB -- Diff_n buffer input (connect directly to top-level port)
);


Enable DIFF_TERM in UCF. 

The DIFF_TERM constraint syntax is documented in the Constraints Guide.

For example:

INST "IO block name" DIFF_TERM = "{TRUE|FALSE}" ;


Enable DIFF_TERM in XDC.

You can see the syntax for this constraint in the Vivado Constraints Guide. 

For example:

set_property DIFF_TERM TRUE  [get_ports SYS_CLK_P]



The property can be set in the Vivado or PlanAhead GUI. You should select the input pair from the port list. There is a checkbox under properties that allows this to be set. 


 


AR# 37171
Date 04/05/2017
Status Active
Type General Article
Devices
  • Spartan-6 LX
  • Spartan-6 LXT
  • Artix-7
  • More
  • Kintex-7
  • Virtex-6 CXT
  • Virtex-6 HXT
  • Virtex-6 LX
  • Virtex-6 LXT
  • Virtex-6 SXT
  • Virtex-6Q
  • Virtex-6QL
  • Virtex-7
  • Virtex-7 HT
  • Zynq-7000
  • Less