Lpc2000

On Wed, Apr 12, 2006 at 02:08:28PM -0600, Michael Anton wrote:
> Most of the implementations you will find for SD actually implement
> the MMC single bit communication method rather than the 4 bit wide
> mode of SD.  This is because the specification for SD is not open
> to the public, and the implementation of it requires a yearly

This isn't the only reason - the 4 bit mode requires that a CRC be
calculated on each bit - i.e. 4 CRCs in parallel. The SPI mode can
be used without CRC, or with only one CRC for the whole
data stream. This makes the 4 bit mode unattractive to implement on
general purpose micros (whereas in a custom ASIC the 4 CRCs are no
big deal).

> may work with MMC cards as well.  But, I think I saw a mention
> somewhere (perhaps on the SanDisk site) that the initialization
> sequence for MMC and SD is slightly different.

It is, but the reduced clock rate is still required, since the SD
card also initializes in an open-drain mode.

The freely available Sandisk documentation is sufficient to implement
SD communication in either mode, without buying the official SD
spec.

Clyde


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Clyde Stubbs                     |            HI-TECH Software
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