MMC & CF memory was Using 3.5' HD drives on CP/M systems

From: Eric Smith <>
Date: Wed Feb 2 18:48:03 2005

jpero wrote:
> What kind of protocol that MMC talks in serial fashion?

MMC protocol, which is a synchronous serial protocol. At the
electrical and timing level it is similar to SPI and Microwire, but
the command set and such are AFAICT not derived from anything else.

If I'm not mistaken, a PDF file of the MMC specification used to be
publicly available at
but I can't find it there now. :-(

Apparently they have now added 4-bit and 8-bit wide interface modes
and higher clock rates (up to 52 MHz) to the latest version of the
standard, probably in response to the SD card specification which
allows 4-bit wide 25 MHz operation. However, it appears to me that
SD has almost completely displaced MMC in the market, so I'm a bit
skeptical that these new MMC modes are going to wind up in many

Received on Wed Feb 02 2005 - 18:48:03 GMT

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