Description

I need more than four IBUFGs to access CLKDLL in my Virtex-E or Spartan-IIE chip, but there are only four IBUFGs available. Is there anything I can do to obtain additional dedicated access to the DLLs?

Solution

Additional dedicated access to the DLLs can be obtained by using the dedicated pins called "IO_LVDS_DLL."  

- Instantiate four IBUFGs inside your design. 

- For the signals that need additional IBUFG, connect IBUFs between the signals and the DLL.  

- Then, lock these signals to the IO_LVDS_DLL pins (see package pin-outs for the pin numbers) for the DLL you want to use.