MPC5554 with external bus interface problem

hi,

     I am using MPC5554 Evaluation Board for testing External SRAM （two slices of IS61WV102416BLL chip ）and configured address 0x20000000. For example, store 0x40000 data in the external memory and then read it out.Why is the value written different from the value read?

Thanking you,

Regards