What happens if the VRN or VRP pins are left unconnected?
When the VRN/VRP pins are left unconnected, the DCI will attempt to match the "infinite impedance".
- For LVDCI and LVDCI_DV2 standards, the output will effectively be 3-stated.
- For most HSTL_DCI, SSTL_DCI, and GTL_DCI standards, the on-chip terminations will be turned completely off. (The exceptions are HSTL_IV_DCI, GTL_DCI, and GTLP_DCI, for which a small part of the termination is turned on as part of the bit stream; therefore, that portion will remain on even when the VRN and VRP pins are disconnected.)
Leaving VRN/VRP disconnected will not damage the device. It will dissipate more power than, for example, a case where the DCI were not turned on, as the DCI control logic would still be active.
Disconnecting the VRN/VRP pins after configuration will increase the impedance of on-chip terminations, but it will not turn the DCI off completely.
NOTE: Some DCI outputs do not require a reference resistor, so they are not affected if the VRN/VRP pins are left unconnected.
Please see (Xilinx Answer 14128) for more information.