have you tried it with another card?


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Gordon Williams
Sent: Friday, March 26, 2004 2:34 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: Multimedia Card Current Problem


I've been playing with a MMC card for data storage, but I have a problem
with current draw under certain circumstances.

When I have the card inserted in the connector and I power up the board, the
current draw on the card is low (in the order of uAs).  It is working as
expected.  I can send commands and it responds.

If I remove the card from the powered up board, wait a second or so and then
reinsert it, the current is now in the order of 20mA.  It is working OK but
it doesn't go into sleep mode when not being accessed.  The current is
always 20mA.

If I quickly remove the card and reinsert, I can get the card to go to
sleep.  The current will drop from 20 mA back to a few uA.  The card
continues to work as expected.

This doesn't have anything to do with the control signals that I am sending
to it with a PIC as it experiences the same problem and symptoms with and
without the PIC installed on the board.

Therefore it has to do with the way the card is being powered up during hot
insertion.

I've come to the conclusion that it is one of two possible problems.
1)  The mmc connector is not perfectly flat.  I botched the installation.
This may mean that the connections are being made in the wrong order.
2)  The rate of voltage rise at the card is different between the board
being powered up and the card being inserted into a hot connector.  When the
board is powered up the voltage rise is in the order of 10's of us, while
with hot insertion it is faster.  There is no droop on the power line that I
can see with a scope during hot insertion.

I hope someone can provide some insight.

Thanks,

Gordon Williams

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