ADSP-21489 external SDRAM memory does not work

hello，

    I  accordance with the design of ADSP-21489 demo board designed a new design, but SDRAM has no effect and other port and functon is normal, Only SDRAM model and demo panels are not the same,I used MT48LC4M16A2-75(64Mb) and demo board used MT48LC16M16A2-6A(256Mb). According to the demo board SDRAM initialization modify.

    I want to ask different types of SDRAM need other special set? Is ADSP-21489 only supports 256Mb SDRAM memory?

Thanks,

Niu