speed of coms between PIC and flash memory (ie mmc)

[homfray]

Roughly how fast could I write a byte of data form a PIC to say an MMC via SPI.

Is SPI the fastest method

I am purely at a initial stage of designing a project and it requires storing data FAST. I would be going at 40MHz. I would appreciate anybodys comments

Thanks
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Nice!!!

[ckielstra]

SPI for MMC cards has a theoretical maximum clock rate of 20MHz, or 2.5Mbyte/s. MMC cards also have the dedicated MMC-bus type which has similar performance as the SPI-bus.

SPI for SD-cards tops at 25MHz or 3Mbytes/sec a little bit faster. Besides the SPI-bus SD cards have another bus, SD-bus, which has 4 datalines and at the same maximum clockspeed this gets you a maximum throughput of 12.5Mbyte/s. I wouldn't recommend SD-cards though because of some nasty design and license issues (like paying US$1500/year for access to documentation).

Fastest are the Compact Flash cards because of their parallel bus.

Actual write speed will be much lower than the above mentioned values because the actual flash writing takes a lot of time. New developments here are strong with new card types comming out every month. For example 45x and 60x cards are out now with 6.4MB/sec and 9.4MB/sec. Strange is the naming of these speeds as they refer to the 150kB/sec speed from a CD-player. Also note that I haven't found these higher speeds for MMC cards yet (only SD and Compact Flash).

From a 32Mbyte Toshiba MMC card specification: