There is an incomplete statement in the 7 Series Configuration User Guide (UG470) in relation to the recommended CFGBVS settings.
Version 1.6 of the document states the following:
"CFGBVS determines the I/O voltage operating range and voltage tolerance for the dedicated configuration bank 0. CFGBVS selects the operating voltage for the dedicated bank 0 at all times in all 7 Series devices."
CFGBVS also determines the I/O configuration for dual-purpose I/O in HR Banks 14 and 15 during FPGA configuration.
When CFGBVS is connected to VCCO of Bank 0, the VCCO of Bank 0 must be 2.5V or 3.3V, and if the I/O in Banks 14 or 15 are used for configuration, then the VCCO for the Banks (14 and 15) must also be 2.5V or 3.3V.
When CFGBVS is connected to GND, the VCCO of Bank 0 must be 1.8V, and if the I/O in Banks 14 or 15 are used for configuration, then the VCCO for the Banks (14 and 15) must also be 1.8V.
Violating this rule will result in configuration failures.
When the following are all true, Bank 14 and Bank 15 I/O use the high-voltage mode:
Banks 14 and 15, when used for configuration, must be supplied with VCCO = 2.5V or 3.3V, matching the voltage on VCCO of Bank 0.
The recommended setup for 1.8V configuration interfaces is:
Note that CFGBVS does not apply to the Virtex-7 HT devices, where bank 0 is an HP bank.
See the following tables for examples.
These tables have also been added to the 7 Series Configuration User Guide (UG470).