I got it ,maybe is the fireware can not handle the signal voltage well , when I try to make a SD CARD work with repetier ,I found that the repetier sdfat.h can not make SPI work ,but arduino original SD.h can... of course this issue happened on arduino due ,mega2560 don't have this problem . So I have reported to repetier on github , and I have try servel SPI speed ,but all fail...I have make the LCD communation with MCU by I2C ,instead of directly....
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