Xilinx LVDS termination resistor

How do you turn the 100 ohm resistor on for an LVDS input? I am using the HDR2 header on an ML402 dev board.

Brad Smallridge aivision.com

Reply to
Brad Smallridge
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Brad,

If the part has them (look in data sheet, or keep reading), it would be the LVDS_DT IO primitive.

LVDS_DT_p for the + terminal, LVDS_DT_N for the - terminal of the diff input pair.

Or, you should be able to see the button in FPGA Editor to turn the termination ON (if it is in the part you have).

The ML402 is for the Virtex 4, and all V4 parts have the DT option.

Aust> How do you turn the 100 ohm resistor on for an LVDS input?

Reply to
Austin Lesea

Hi Austin,

Can you spell this out for me a little clearer. I am a little slow.

I went to the FPGA editor to look at the inputs. There is a connection from the N input to the P input. And an ouput of the P going off to the rest of the fabric.

Going into the P input, I see a mark next to LVDS_25 and DIFF_TERM FALSE. Should DIFF_TERM be TRUE? The software would not allow me to make a change.

I can not find LVDS_DT in the ISE7.1 online documentation libraries guide.

Thanks for your help. This has been an issue for several days now.

Brad Smallridge aivision.com

Reply to
Brad Smallridge

OK. You add this to your UCF file:

INST cam1_x0_ibufd_inst DIFF_TERM = TRUE; INST cam1_x1_ibufd_inst DIFF_TERM = TRUE; INST cam1_x2_ibufd_inst DIFF_TERM = TRUE; INST cam1_x3_ibufd_inst DIFF_TERM = TRUE; INST cam1_xclk_ibufd_inst DIFF_TERM = TRUE;

Reply to
Brad Smallridge

Howdy Brad,

Not surprising that you were confused by this. The below answer record mentions that "DT" is available on V2Pro and V4. Except that on the V4 it is invoked in an entirely different way than it is was on the V2Pro:

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As you can see, you must use LVDS_25_DT for V2Pro, and you must use DIFF_TERM attribute on your LVDS_25 on V4 - so if a design is retargetted from V2Pro to V4, it would run into the exact same problem that you did.

Have fun,

Marc

Reply to
Marc Randolph

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