Messages in this thread | | | Subject | RE: MMC: Card detection through pin CD/DAT3 issue | Date | Tue, 18 Mar 2008 13:24:33 +0100 | From | "Wappler Marcel" <> |
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Hi Pierre,
>> With this detection scheme I have some dificulties togehter >> with the internal working of the current MMC stack: >> The controller cannot detect a newly inserted card if the card power >> is switched of. This is due to the fact that the SD card applies the >> internal card detection pull up after it powered up. If there is no >> power -> no powering up -> no pull up. (besides the fact that a pull >> up needs power to for doing its work :-) ) >>
> Then you have broken hardware. The specs clearly state that the > controller must be able to detect cards without powering up the > cards. Also, the cards must implement the pull-up in a way that > behaves like a resistor. So there should be no requirement for > full power there either.
I have found this requirement in the SD host controller spec: "The card detect is active regardless of the SD Bus Power."
I wonder how the card should be able to pull up the CD/DAT3 Pad to VCC if its only VCC pad is not connected to VCC due to the fact that the host controller has switched off the cards power - any idea how this could be managed?
There is a SD card spec section somewhere which statet that: "If one of the supply pins (VDD or VSS) is not connected properly, then the current is drawn through a data line to supply the card."
Maybe this is the key in understanding ho the pull up without VCC connected works?
Thanks, marcel
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