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Explorer
Explorer
1,839 Views
Registered: ‎05-14-2017

in Vivado I/O port planning window, how to select 50-ohm Diff termination for input lvds

I'm using ibufds for a lvds_25 signal type and would like to implement the FPGA internal 50-ohm termination because I didn't design any 50-ohm termination on my board.

Within vivado, in the I/O port window, under the IN_TERM column, there is no drop down menu to select the 50-ohm termination option. There is another column called off-chip termination and there is only one option called NONE which is selected and use in this column

 

How would I specify Vivado to use 50-ohm termination for my lvds input ?

 

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3 Replies
Voyager
Voyager
1,827 Views
Registered: ‎06-24-2013

Re: in Vivado I/O port planning window, how to select 50-ohm Diff termination for input lvds

Hey @tchin123,

 

... in the I/O port window, under the IN_TERM column ...

The IN_TERM column is for selecting the Uncalibrated Split Termination in High-Range I/O Banks

 

... another column called off-chip termination ...

This is to describe external termination to the tools.

 

How would I specify Vivado to use 50-ohm termination for my lvds input?

You can't, but you probably do not want to do that anyway, because LVDS termination is 100 Ohm.

 

What you are looking for is the DIFF_TERM which can be configured as constraint or as attribute in VHDL and Verilog.

 

Hope this helps,

Herbert

-------------- Yes, I do this for fun!
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Explorer
Explorer
1,791 Views
Registered: ‎05-14-2017

Re: in Vivado I/O port planning window, how to select 50-ohm Diff termination for input lvds

Thx for the information. You are right, I mean 100-ohm not 50 ohm.

 

I new to Vivado and not use to the constraint syntax therefore I rely on the vivado gui to set all my constraints for now.

therefore if I have an input differential lvds signals called miso-p and miso-n that requires 100-ohm internal termination between them.  The I/o planner doesn't provide the option to set them? Is there another vivado window to do this.

i thought if I use lvds input the tool would automatically insert them since this is a necessity for them.

 

I realizes the termination is missing when I scope these LVDS signals and they actually went to the external device driver's voltage rail of +3.3 and ground. I believe this confirm there is no termination attached to the fpga  ibufds.

if the vivado GUI doesn't allow the user to declare the termination, then what is the proper syntax to declare them in my Xdc file?

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Voyager
Voyager
1,772 Views
Registered: ‎06-24-2013

Re: in Vivado I/O port planning window, how to select 50-ohm Diff termination for input lvds

Hey @tchin123,

 

Thx for the information.

You're welcome!

 

The I/o planner doesn't provide the option to set them?

When you select the 'I/O Ports Tab' at the bottom and pick your port, then you can select I/O Port Properties from the context menu (right mouse button), there the 'Properties' Tab will have an entry 'DIFF_TERM' where you can check the box right to it.

 

i thought if I use lvds input the tool would automatically insert them since this is a necessity for them.

Termination could as well be external, as you noted in the very first port, so it's an option.

 

what is the proper syntax to declare them in my Xdc file?

set_property DIFF_TERM 1 [get_ports miso*]

Note that you can see the TCL commands in the 'Tcl Console' when you check or uncheck the DIFF_TERM attribute.

 

Hope this helps,

Herbert

-------------- Yes, I do this for fun!