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LVDS Input buffer in VHDL (ISE)

I'm trying to instantiate some LVDS input buffers in VHDL using the following code:

LVDS_lines: for i in 0 to 19 generate Inputs_LVDS : IBUFDS_LVDS_25_DT -- LVDS input buffer with Rterm active port map ( I => data_lvds_in_p(i), IB => data_lvds_in_n(i), O => data_lvds_in_sig(i)); end generate;

but ISE doesn't seem to recognise IBUFDS_LVDS_25_DT as it just gives me an Undefined Symbol error. Missing off the DT is OK but I need the termination resistor to be active so it has to be this buffer.

If anyone has any ideas what's wrong I'd be grateful to hear.

TIA.

Rog.

Reply to
Roger
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I also started to coding LVDS buffers, but for verilog. module xxx ( input gclk_p, input gclk_n); wire gclk; IBUFGDS ibuf1(.O(gclk),.I(gclk_p),.IB(gclk_n)); endmodule selected automatically the desired LVDS_25 (from the .map file): P76|gclk_p|DIFFM|IO_L32P_5/GCLK2|INPUT|LVDS_25|5||||NONE||LOCATED||NO|NONE| P77|gclk_n|DIFFS|IO_L32N_5/GCLK3|INPUT|LVDS_25|5||||NONE||LOCATED||NO|NONE|

Bye

--
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
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Reply to
Uwe Bonnes

Is this Virtex-4?

Reply to
Brad Smallridge

You didn't mention what part you are using. But generally, Xilinx refers to it's termination scheme as "Digitally Controlled Impedance" IIRC, and the IO name is IBUFDS_LVDS_25_DCI.

Reply to
Duane Clark

The part is Virtex IIPro. It's not the DCI I'm looking for, it's the on-chip

100R termination.

Thanks.

Roger.

Reply to
Roger

What version of ISE?

Are you using the unisim library like this: library unisim; use unisim.vcomponents.all;

Or, defining the component yourself?

Instead of using the named suffix I/O buffer, try sticking an IO_STANDARD of LVDS_25_DT on an input buffer of type IBUF{G}DS

See also Answer Record 17244

Brian

Reply to
Brian Davis

Brian,

Thanks, this was really useful.

I'm using version 7.1 of ISE and yes, I have the unisim library lines in the code.

I used the generic ... IOSTANDARD = LVDS_25_DT on an IBUFDS as you suggested and it worked! I don't know why and probably never will but it allows me to progress with the design now. Thanks again.

Roger.

Reply to
Roger

I had the same issue. The IBUFDS_LVDS_25_DT is shown in the library package but XST doesn't recognize it. I ended up doing what you did. Chuck

Reply to
cwoodring

Glad that worked.

And, now I know what to change when I switch to 7.1 !

I haven't updated from 6.3 yet at home to create a test case, but I've had problems with attributes not sticking to diff. buffers before ( especially the _DIFF_OUT variants )

I think Xilinx is getting away from the named suffixes for the newer families, so perhaps they broke something in the tool flow.

Brian

Reply to
Brian Davis

Thanks everyone. This has been useful for me and others.

Roger.

Reply to
Roger

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