When a DCM is used in a 2V4000 device, you must use the BitGen option described below to guarantee operation up to the maximum frequency specification.
This BitGen option should be used only if the CLKIN frequency exceeds 300 MHz (-4 speed grade) or 350 MHz (-5 speed grade). Otherwise, the LOCKED signal may go low during operation, or it may fail to go high in the first place.
- The 2V4000 devices released with the enhanced multiplier do NOT require this option. However, using the BitGen option will cause no harm to these devices.
- For information on identifying 2V4000 with enhanced multiplier, reference (Xilinx Answer 14339).
The required BitGen option is:
-g vbg_sel2:1 -g vbg_sel1:1 -g vbg_sel0:1
The following is an example command line:
bitgen -g vbg_sel2:1 -g vbg_sel1:1 -g vbg_sel0:1 [other option] <design.ncd>
In Project Navigator, you can set this option in the "Other BitGen Command Line Options" text field. This field is available after the environment variable "XIL_PROJNAV_BITGEN_OPTION" is set. This option is available beginning with the 4.2i software release.