10-28-2010 01:13 AM
I am trying to output clock that is recovered by the GTP (RecClk) to the output pins.
RecClk is connected to BUFG, so I am trying to output global clock signal.
I want to make a differential output for this clock, but when I tryed to use OBUFDS for it, Mapper said me:
ERROR:LIT:544 - BUFDS symbol
(output signal=GTP_RefClks<1>) can only drive a GTPA1_DUAL's CLK00, CLK01,
CLK10, or CLK11 pins. Please modify the design to avoid an unroutable
So, is it possible to output global clock as differential signal?
Thank you in advance.
10-28-2010 02:53 AM
you said that ref_clk is connected to a global Clock buffer (BUFG) . Normaly these routes are special and can not be accessed for other purposes.
So, you need to take the signal from the clock net. It may be difficult to connect a OBUFDS directly to a Clock net,but you can use one or two ODDR2 modules to "reconstruct" the clock signal.
Instantiate a ODDR2 with a constant 1 on the data input that is affiliated with the normal clock and a constant '0' to the data input thats affiliated with the inverted clock. drive the clocks from the clock net that has ref_clk on it.
If necessary use a second ODDR2 with inverted data inputs to create the inverted input for the OBUFDS. (I'm not sure about the necessary inputs of the OBUFDS).
But maybe there is a simpler solution to it.
Have a nice synthesis
10-28-2010 03:32 AM - edited 10-28-2010 03:39 AM
To what pins you are trying to connect those differential signals ? user sma A3 B3 ?
Try using bufio2fb insted of bufg and check attributes of obufds. Or try place two bufgs after obufds ))
08-16-2012 12:03 AM
it works when i used bufio2fb insted of bufg. Now i can connect clock directly to a OBUFDS pin.