I have interfaced 256Mb sdcard with stm32f051 using FATFS driver, find_volume() function is giving FR_NO_FILESYSTEM response because ld_word(fs->win + BS_55AA) != 0xAA55. Please give me some solution for this issue.
Your description does not allow to provide a closer reply.
My statement refers to MDK 5.28a, which today is our latest release.
The Pack Installer of MDK offers for many ST devices demonstrating FileSystem example projects (i.e."File System Demo" for STM32F4):
http://www2.keil.com/mdk5/packinstaller/
Compare with one of these projects your implementation.
See also our "File System Component Documentation" at:
https://www.keil.com/pack/doc/mw/FileSystem/html/index.html
Note - File System access as part of the MDK-Middleware requires either MDK-Pro or MDK-Plus:
http://www2.keil.com/mdk5/middleware
http://www2.keil.com/mdk5/selector