Thank you for the advice! But i have another issue when using the SdFat library. I tested the library with the ReadWriteSdFat example. In the Serial Com, it showed "Writing to test.txt...done.", "error: opening test.txt for read failed", "SD errorCode: 0x13,0x0". When i used another SD card, same error pops up with a different error code as 0x6,0x1. Does anyone know what is the meaning about this?