The port mapping must specify p and n sides of the input as you have done.
The UCF needs to have the IOSTANDARD = LVDS_x set and only the P side pin
needs a LOC constraint. The tools will pick up the IO standard correctly
and place the N side on the correct corresponding P pin.
"Morgan" <morgank@lanl.gov> wrote in message
news:1165424528.893445.244150@l12g2000cwl.googlegroups.com...
>I apologize if this questions has been answered already. I was unable
> to find an answer in my search through this group.
>
> If you have any experience using LVDS with Xilinx FPGAs, please help.
>
> Q: If I have a LVDS input, must my top-level entity specify both the N
> and P ports, or is there a way to specify that a port should use LVDS
> in a constraint file and have the Xilinx tools infer the correct
> buffers?
>
> I know something to this effect works:
>
> ...
> input_p : std_logic;
> input_n : std_logic;
> ...
> port map (
> I => input_p,
> IB => input_n,
> O => internal_single_ended_signal);
>
>
> But, is there a way to just have the following (plus specify that input
> is LVDS in a constraints file) and have the xilinx tools infer what is
> in the code above?:
>
> ...
> input : std_logic;
> ...
>
>
> Thank you in advance for your help.
>
Reply by Morgan●December 6, 20062006-12-06
I apologize if this questions has been answered already. I was unable
to find an answer in my search through this group.
If you have any experience using LVDS with Xilinx FPGAs, please help.
Q: If I have a LVDS input, must my top-level entity specify both the N
and P ports, or is there a way to specify that a port should use LVDS
in a constraint file and have the Xilinx tools infer the correct
buffers?
I know something to this effect works:
...
input_p : std_logic;
input_n : std_logic;
...
port map (
I => input_p,
IB => input_n,
O => internal_single_ended_signal);
But, is there a way to just have the following (plus specify that input
is LVDS in a constraints file) and have the xilinx tools infer what is
in the code above?:
...
input : std_logic;
...
Thank you in advance for your help.