linux-kernel - RE: MMC: Card detection through pin CD/DAT3 issue

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Date:	Wed, 19 Mar 2008 00:08:36 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Wappler Marcel <Marcel.Wappler@...dgeco.net>,
	Pierre Ossman <drzeus-mmc@...eus.cx>,
	linux-kernel@...r.kernel.org
Subject: RE: MMC: Card detection through pin CD/DAT3 issue

Wappler Marcel <Marcel.Wappler@...dgeco.net> wrote:

> 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?

If the VCC pin is connected to 0 V, the "pullup" will pull down to 0 V.
If the controller reverses it's logic while VCC=0, it might work.

The controller might alternatively switch all pins (except the pullup) to
VCC, which would look to the card like switching all pins to 0V, but
detection by pullup would still work.

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