There are three methods to delay configuration on the Spartan-3AN
(1) Hold INIT low
This method prevents the M[2:0] pins being sampled and will delay the start of any configuration operations
(2) Hold PROG low
This method will result in the device being repeatedly put into housecleaning state. This will delay the start of any configuration operations but will cause extra power to be consumed.
(3) Hold DONE low
This will delay the device at startup after all configuration data has loaded and the CRC check has been passed. This method is dependent on the Bitgen Startup options. In the default order of DONE =4, GWE = 5 and GTS = 6 this method is valid. If GWE and GTS are before the DONE state of the startup, the device will be operational despite DONE being held low.
Note: Special care should be taken with the DONE transition in this state. DONE should transition monotonically with a rise time less than one CCLK period. If there is a slow DONE transition, the device may not complete startup. If there is a non-monotonic or noisy DONE transition, thiscan result in the device completing startup and then functioning incorrectly or outputs not toggling.