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AR# 14196

Virtex-II, DCI/XCITE - What happens if the VRN or VRP pins are left unconnected?

Description

What happens if the VRN or VRP pins are left unconnected?

Solution

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.

AR# 14196
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article