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Thanks Magnus! RTFM, as they say. I've wasted a lot of time
building speed switching circuits in my life, for no reason!<br>
<br>
On 02/13/2016 05:35 PM, Magnus Karlsson wrote:<br>
<blockquote cite="mid:56BFD9DC.9010307@saanlima.com" type="cite">
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<div class="moz-cite-prefix">>> Ignoring the multiplicity of
standards overlaid onto SD / MMC, you can talk to all cards with
a simple SPI port; the only complication is the requirement to
go slow until a faster rate is negotiated.<br>
<br>
This is a common misunderstanding. In SPI mode there is no need
to go slow initially, you can go at full speed right away. The
need for slow speed is in SD or MMC mode where the pins are
initially open-drain in order to support multiple cards on the
same bus. In SPI mode the signaling is always push-pull and you
can clock the card at typically up to 25 MHz from the start.<br>
<br>
See Appendix A in this document <a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="http://www.circlemud.org/jelson/sdcard/SDCardStandardv1.9.pdf">http://www.circlemud.org/jelson/sdcard/SDCardStandardv1.9.pdf</a><br>
<br>
<i>Timing specifications </i><i><br>
</i><i>Design engineers must meet the rise, fall, setup, hold,
and other SD Card and MultiMediaCard bus timing
specifications. If they want to support MultiMediaCards in
their design, the clock speed should be controllable by the
host. This is due to the MultiMediaCard's open-drain mode;
the MultiMediaCard powers up in the open-drain mode and cannot
handle a clock faster than 400 Khz. Once the MultiMediaCard
completes the initialization process, the card switches to the
push-pull mode. In the push-pull mode the MultiMediaCard can
run at the maximum clock speed<br>
</i><br>
Magnus<br>
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