MCU doesnt identify the uSD

[chunjonas]

Hi All,

i am doing a project to use a mcu which has a peripherial uSD to store some datas. Right now i have two uSDs, ic name them A and B. they both are formated with the same PC as FAT32 file system.
i have wrotten the software for the communication process. the software can access uSD A to read and write files. but the software cannt identify the uSD B!

accrding the description of FAT32 the first sector of the uSD should be MBR, if MBR not exsists, then should be DBR.
But either MBR or DBR the last two chars of first sector must be 0x55,0xAA! i mean the 510. and 511. chars!

i read these two chars: from A they are 0x55,0xAA, but from B there are 0x01,0x00 NOT 0x55 0xAA! i dont understand why it is that? because these were formattied in the same way(i think ao).

if the uSD B was bad, why the PC and cell phone can identify it? can also write and read file? or i have missunderstood that it maybe the last two chars not must be 0x55 0xAA?

waiting for your answers regardly....