[U-Boot] A problem about using the nand command

[li guohu]

Hello, everyone!
I find a strange problem when I use the u-boot command. I list the command I used in the u-boot command line as follows.
 
nand erase
nand read 0x2000000 0x0 0x800
md 0x2000000
 
I should see 2K bytes of "0xFF" because I have erase the whole nand flash device. Actually, I find a "0xFD" in one address. 
Then I try display some other contend of the nand flash. I can also find one "0xFD" in every 2K address space. It is so strange.
By the way, I find that the offsets of the addresses of the one "0xFD" from the start of the page are the same. The size of one flash page is 2K bytes.
Are the driver of the nand flash in the u-boot wrong? Or are there some other problems?