AR# 8145: Virtex Configuration - What are valid VCCOs for Configuration Banks (2 and 3)?
Virtex Configuration - What are valid VCCOs for Configuration Banks (2 and 3)?
Keywords: Virtex, VCCO, configuration, voltage
General Description: What VCCOs are valid to be put on Configuration Banks 2 and 3? (The configuration pins are on these banks.)
Virtex-E inputs are sourced from the VCCO voltage, per the Virtex-E data sheet. If the VCCO is lowered below 3.0V (in this case, 2.5V), then the standard will change from LVTTL to LVCOMS2. Thus, the input threshold will change from 2.0V to 1.7V. Because of this, Xilinx does not recommend that a Virtex-E device be interfaced to an 18V00 PROM with a VCCO that is < 3.3V.
For Virtex, the inputs are sourced from VCCINT, so the input buffer will not be a problem. 1.8V is also a valid VCCO for Virtex on Banks 2 and 3.
However, for both devices, the device will drive rail-to-rail, so it is important to ensure that devices interfacing with the configuration logic will be able to handle the outputs and register the proper logic highs (CCLK if Master Serial, BUSY if SelectMAP, etc.).