Hi Kunal,
In order to access to files of a USB stick, it is required to have an embedded File System, in addition to the Mass Storage Class support of USB Host. You could take a look at the following link:
https://www.embeddedrelated.com/showthread/lpc2000/54659-1.php
Additionally, it is also required to implement a bootloader. The application notes provide guidelines on the external memory access on LPC24xx, and a similar application that you are asking, but implemented on ColdFire and Kinetis microcontrollers:
https://www.nxp.com/docs/en/application-note/AN10950.pdf
https://www.nxp.com/docs/en/application-note/AN4368.pdf
Hope this will be useful for you.
Best regards!
/Carlos
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