Can SDIO cards be in a shared bus topology

Question

I know MMC cards can share a bus and it seems like it should work with SD/SDIO cards as well. However, I've found conflicting information on the web and the simplified specs at sdcard.org talk about doing the card identification using "each cards individual CMD line."

If I manage to assign two SDIO cards different RCA (addresses) by using some trickery with powering up in the right order or using some form of muxing, shouldn't I be able to use them on a shared bus?

Thanks, Andrew

Answer 1

From what I have read and know of SDIO, you should be able to multiplex the CMD line to the cards and share the data lines. I don't believe the DAT lines will be used at all except in response to a command.

According to http://www.embeddedrelated.com/usenet/embedded/show/69909-1.php, one poster explains how the ALL_SEND_CID command works on a multicard bus. In this explanation, no lines are multiplexed. I'm not sure how the initialization sequence would work in this topology and it's not explained.

I know once the card is identified and given the relative address you can select and deselect the card for handling commands.

Hopefully this helps.