What does the DSSEN pin on the DCM do?
The DSSEN pin and the DSS_MODE attribute were prepared to support the Digital Spread Spectrum (DSS) feature in the DCM. This feature is not supported. However, the DSSEN pin remains an input pin in the DCM primitive to maintain compatibility with all DCM library versions.
For all designs using DCM, please connect the DSSEN pin to GND and leave DSS_MODE at its default value. If you are using Architecture Wizard (DCM/Clocking Wizard), this connection has been done automatically.