In prior devices families, the PROG or the INIT pins can be held Low at power-up to delay configuration. In the7 series devices, the PROG pin is edge-sensitive as opposed to level-sensitive; therefore, holding this pin Low at power-up does not continue to delay configuration.
To delay configuration, hold the INIT pin Low. INIT is an open drain driver and requires a pullup on the pin to pull the pin High once it is released by the device. The device only drives the pin Low, and then releases the pin when the device is ready to start configuration. The INIT pin must then go High for the mode pins to be sampled and the configuration process to begin.