1. Home
  2. Field-Programmable Gate Arrays
  3. Specifying LVDS I/O's in Xilinx FPGA's

Specifying LVDS I/O's in Xilinx FPGA's

Hi,

Can someone please point me in the right direction.

I attempted to define my LVDS inputs via the UCF file for my Xilinx spartan xc3s1500.

NET data_in LOC = F19 | IOSTANDARD = LVDS_25 ;

the Xilinx answer record impies that this will work OK.

formatting link

Unfortunately I get the following warning, and the input is set to a standard LVCMOS25.

WARNING:Pack:946 - The I/O component data_in has an illegal I/O standard value. Components of type IOB do not support I/O standard LVDS_25. Please correct the IOSTANDARD property value.

I am using ISE 8.2 (Release 8.2.03i Map I.34)

Any ideas what I am doing wrong? Do I need to istantiate the I/O buffers?

Thanks for any input,

Steven

Reply to
moogyd
Loading thread data ...

Hi Steven, I usually instantiate the IBUFDS (see libraries guide) in my HDL and go from there. Don't forget your terminations...

INST "LVDS_P" DIFF_TERM = TRUE; INST "LVDS_N" DIFF_TERM = TRUE;

Also, the tools sometimes get their knickers in a twist about 3.3V and 2.5V banks. Googling should solve that for you.

HTH., Syms.

Reply to
Symon

Do you realize that the LVDS *is* a differential signals and requires two pins to be defined in the design file?

Reply to
John_H

defparam buf_100.IOSTANDARD = "LVPECL_25"; defparam buf_103.IOSTANDARD = "LVPECL_25";

IBUFDS buf_100 (.I(pad_dsp_adc_fsync_cmd_p), .IB (pad_dsp_adc_fsync_cmd_n), .O(dsp_adc_fsync_cmd) ); OBUFDS buf_103 (.I(adc_dsp_sdo_q_p), .O(pad_adc_dsp_sdo_p), .OB(pad_adc_dsp_sdo_n) );

Always check the following doc file for good reference to primitives : /Xilinx/doc/useglish/books/lib/lib.pdf

-- Regards, John Retta Owner and Designer Retta Technical Consulting Inc. Colorado Based Xilinx Consultant

email : snipped-for-privacy@rtc-inc.com web :

formatting link

Reply to
John Retta

Thanks for all the responses.

I instantiated the buffers directly in the HDL with no problems.

I know that the S/W is "free", but I don't know why the documentation implies that you can just specify the buffers in the UCF (I had the same issue with BUFG's).

Anyway, thanks again,

Steven

Reply to
moogyd

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.