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power down & on mmc by micro

 
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power down & on mmc by micro
PostPosted: Tue Mar 29, 2005 10:17 am     Reply with quote
when initialing the mmc card heve need to power down & on my micro or not?( i see some code that do that)
TSchultz



Joined: 08 Sep 2003
Posts: 66
Location: Toronto, Canada

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PostPosted: Tue Mar 29, 2005 2:02 pm     Reply with quote
I have seen instances where the MMC needs to be powered OFF then back ON to force a hardware reset of the device. Normally you can just use the software reset sequence but I have encountered instances where it was not enough.

I would suggest a P channel FET on the supply to the MMC, and the pull-ups on the data lines. You can then turn OFF the FET and set the I/O's to input to force the MMC in an OFF state, then turn the FET ON and re-configure the I/O's to turn on the MMC card. This then needs to be followed by a software command sequence to initialize the MMC in SPI mode.

Take care if you intend to operate the PIC from 5V, most of the MMC cards cannot be powered at 5V and their I/O's are not 5V tolerant.
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