Re: Micro-SD card initialisation-problem


"R.Wieser" <address@xxxxxxxxxxxxx> wrote in message
news:4880ddc3$0$14361$e4fe514c@xxxxxxxxxxxxxxxxx
Hello Arie,

Those resistor values are much too high to give clean edges
on the clock input of the SD-card.

I got those resistor-values off the Web actually, together with a "it
works
for me" assurance.

Depends on the input capacitance of the card, cable length, etc...
Someone might have been lucky.

Allso, making those resistors 10 times lower would mean you would actually
be drawing current from the printer-port, which (ofcourse) allso has a
resistor in its high-level output circuit.

That would mean two things : to many ports all sourcing a current of about
10 mili-amps could heat-up the driver-chip (controller nowerdays) quite
nicely, and would allso bring the voltage-drop over the internal resistor
into play.

Yes. that's why I always use buffers - or a spec'ed driver and short
connections.

A slow edge will cause noise glitches in the clock signal.

Although the signals do show a few spikes here-and-there (I did put a
scope
on the signals) its not as bad as the chips own output-signal. :-)

Clock edges are most important - rise and fall times must be within spec,
and the data / cmd lines stable around them.
Or the card must use schmitttrigger inputs on the clock. I'm not sure the
spec requires that.

And VERY short lines between buffer and the card clock input.

:-) That was what I was thinking to, until I saw the clean signals on the
scope (currently I've got a meter-and-a-half printer-cable betweenthe PC
and
the sd-card).

Without reflections? Or are you using a 10 MHz scope? The card allows up to
25 MHz clock, normally that means edges should be < 5 ns rise/fall time. You
cannot see noise / glitches on a low-bandwidth scope.

Allso: I currently got one of the two MicroSD cards to work : the Sandisk
one (the other still refuses to initialize). I've just my first sectors
worth of data (the MBR, which seems to be quite empty apart from the
partition-table).

I'll first see if I can get the SanDisk card to do what I want, and than
try
to figure out why the other card does not want to work. I'll maybe even
put
some line-drivers to the signals (both ways) to see if it changes
anything.
But as I allready mentioned, I *can* write commands to the (stubborn) card
(CMD58 for example) and read the replies. Even multiple times in quick
succession.

Thanks for your suggestion though.

Regards,
Rudy Wieser

Success!

Arie de Muynck



.

Relevant Pages

  • Re: Micro-SD card initialisation-problem
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