The hardware interface to the SD card should not use a resistor based
level shifter. SdFat sets the SPI bus frequency to 8 MHz which results
in signal rise times that are too slow for the edge detectors in many
newer SD card controllers when resistor voltage dividers are used.
The 5 to 3.3 V level shifter for 5 V arduinos should be IC based like
the 74HC4050N based circuit shown in the file SdLevel.png. The
Adafruit Wave Shield uses a 74AHC125N. Gravitech sells SD and MicroSD
Card Adapters based on the 74LCX245.
Ответить с цитированием