When I perform a SelectMAP configuration with an encrypted bitstream, BUSY asserts at a lower speed than the 66 MHz specification. What is the reason for this?
Extra processing time is needed when the bitstream is encrypted. Consequently, BUSY handshaking is required for encrypted bitstreams at a lower speed than for non-encrypted bitstreams.
The maximum speed at which a Virtex-II/-II Pro device can be configured via SelectMAP without BUSY handshaking is 5 MHz.