Question: SDRAM with a 12 ns speed could work with the TMS320C80 at 50 MHz ?

Answer: The 3 ns setup time should not affect the ability of the SDRAM to interface directly to the C80 at 50 MHz. If using buffers and transceivers as described in the appnote, the setup times for data and address will be violated by the amount by which the 3 ns time exceeds that of the C80 (assuming worst case loading).