Boot from SPI can not find the AT45DB642

hello

I switch  the bf537 to boot from SPI ,and the device is AT45DB642. but it seems the processor can not find the AT45DB642.

The following  is what I had done:

first of all, I power up the board ,,but there is no respond. I check the datasheet ,

it says The on-chip boot ROM, Sends the read command, 0x03, on the MOSI pin then does a dummy read of the MISO pin.

so that ,I  tested  the MOSI and MISO pin , I found that ,there is no signal  but just high level.

and when I test the MOSI and MISO pin on other people`s board (they are using AT45DB321), I can test the  signal just liek the datasheet said!!

so can someone  tell  me  why my board can not  found the device??  Or offer me some information to solve this problem?

thank you !!