Home/ Questions/Q 8928689
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-15T08:30:08+00:00

I have a clock input to the fan-out buffer which drives LVDS input to

  • 0

I have a clock input to the fan-out buffer which drives LVDS input to the bottom edge of PLL input. There are two pins – AJ19 (active high) and a complementary AK19 pin (active low). I am only interested in AJ19, so my top level module looks like this:

module top(clk, ...);
...
endmodule

Here is my pinout for a clk:

set_instance_assignment -name IO_STANDARD LVDS -to clk
set_location_assignment PIN_AJ19 -to clk
set_location_assignment PIN_AK19 -to "clk(n)"

So far so good, but fitter is generating a very annoying warning that drives me crazy:

Warning (15714): Some pins have incomplete I/O assignments. Refer to the I/O Assignment Warnings report for details
Warning (176674): Following 1 pins are differential I/O pins but do not have their complement pins. Hence, the Fitter automatically created the complement pins.
    Warning (176118): Pin "clk" is a differential I/O pin but does not have its complement pin. Hence, fitter automatically created the complement pin "clk(n)"

Altera’s knowledge base suggested to actually define the clock as a pair (i.e. input wire [1:0] clk) to remove the warning. That doesn’t quite help because then you get another warning, saying that input pin does not drive any logic.

I have tried to disable this warning using // altera message_off 176118. That results in error because “176118” is not a valid message ID.

Any suggestions on how to solve this problem?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    See Altera “Designing with Low-Level Primitives User Guide” for primitive details and templates
    http://www.altera.co.uk/literature/ug/ug_low_level.pdf

    Example of wrapping top level block:

    module top_wrap (
    ...
    input wire refclk,  input wire refclk_n,
  );

    // differential input buffers
  wire int_refclk;
  ALT_INBUF_DIFF inbuf_refclk (
    .i (refclk),
    .ibar (refclk_n),
    .o(int_refclk),
  );

  top wrapped (
      .refclk( int_refclk),
      ...
  )
endmodule
    • 0