I successfully wire an SD Card Reader to the SPI pins of an Arduino UNO R3. I then run a program that writes one line into a file on the SDCard. I insert the SD Card in the card reader of my desktop computer and all is fine.
Now, I plug in an Arduino Usb Host Shield 2.0, re-connect the SD card reader and the same program fails on SD.begin(CS_PIN).
Yes, CS_PIN is another pin than 10 (which should be the one used by the USB host shield), and yes my test program is really simple and only includes SD.h (the same happens with SdFat.h). I have already tried disabling the pin 10 before initializing the SD Card reader via SD.begin(CS_PIN) - through pinMode(10, OUTPUT); digitalWrite(10, HIGH); .
How can this be? Is the USB host shield writing something to the SPI bus in parallel while the SD Card reader gets initialized?