Recently in the use of card reader, need has been connected to the development board, use it after the system can detect normal card reader device for/dev/SDB, provides sd card can't identify the sdb1 partitions, also do not have any printed information,
But the SD card before start receiving card reader can identify normal sdb1 partitions,
Measuring the DELECT the SD card pin, the default for the high level, access to low level after the SD card, there is a level of change,
What is the reasons of this phenomenon? How to access sd card after electricity can identify to it?