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SDcard pullups

PostPosted: Mon Oct 27, 2008 12:48 am
by barmagan
I made a payload card uses SD card to write something(~15KB) and FM430 turns its power on/off. When FM tries to power down payload its not completely powered down. I think SD card pullups keeps on supplying the payload from Vcc.
I know SDIO spec says there should be pullups on data pins. Do we really need pullups in SPI mode? Generally SPI works without pullups I think. During payload tests I didn't use pullups. And successfully wrote to a external SD card.
Did anyone tried to remove pullups on FM430? Does it work?

If not, what do suggest for isolation? Payload just uses SD card


Re: SDcard pullups

PostPosted: Mon Oct 27, 2008 4:29 am
by aek
1) I'm not comfortable with SD running without pullups. The SD Card spec clearly shows the pullups.

2) I did tests with the Rev C CSK SD Card interface scheme in terms of looking at what was happening to an unpowered card that still "sees" the activity on its SDIO pins ... I found that different brands of cards saw their SDIO pins float at different values ... but all were below the reset voltage of the spec, so in theory these cards were truly "asleep" while unpowered.

3) I think using active isolation is a better solution, and the upcoming Rev D versions of the CSK use active isolation (and pullups).

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Re: SDcard pullups

PostPosted: Tue Nov 04, 2008 1:53 am
by barmagan
During SD card communication, does SD card becomes master sometime?

If not is SN74HC244 suitable for this isolation? (one way)

Or should I use an analog switch (two way)?


Re: SDcard pullups

PostPosted: Tue Nov 04, 2008 5:49 am
by aek
1. No.

2. You could do that.

3. You could also do that.

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Re: SDcard pullups

PostPosted: Tue Nov 04, 2008 6:43 am
by barmagan
Thanks AEK,
I used 74HC244 and solved the problem.

B.Armagan