DCIUpdateMode is a configuration option that can override control of how often the DCI circuit updates the impedance matching to the VRP reference resistor. This option defaults to ASREQUIRED in the Xilinx implementation tools. The settings for the DCIUpdateMode configuration option are:
•ASREQUIRED: Initial impedance calibration is made at device initialization, and dynamic impedance adjustments are made as needed throughout device operation (default).
•QUIET: Impedance calibration is done once at device initialization, or each time the RST pin is asserted on the DCIRESET primitive for designs that include this primitive.
RECOMMENDED: It is strongly recommended that the DCIUpdateMode option be kept with the default value of ASREQUIRED so that the DCI circuitry is allowed to operate normally.