Speed information on SD card FAT

Hi, Where can I find the speed information of a SD card on its FAT ? I think this info must be present, because all card PC readers can read any card without any problems.

Thanks for your replies.

Yvan

Reply to
Yvan BOURNE
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Well, the SD cards are specified for 20MBit or so on the SPI port as far as I remember. How quick your controller is with feeding the SPI is beyond my guess.

Rene

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Ing.Buero R.Tschaggelar - http://www.ibrtses.com
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Reply to
Rene Tschaggelar

I suspect the OP meant 'Quick Start Guide' Rocky

Reply to
Rocky

The Fclk on the SPI bus is specified for 25MHz max. But I have different comportment between various SD card. Some card function correctly, others make some write errors at sectors changes. If I put my Fclk slower, these problems disappear...

Yvan

Reply to
Yvan BOURNE

The SD card spec is 25 MHz so if a card can't handle that then they're out of spec. However, you need to look at the signal integrity of the connection. The data lines should have very low capacitance and pull-ups. It might be a good idea to turn on CRC chacking and generate and check that all is well.

Peter

Reply to
Peter Dickerson

The FAT would be the wrong place to look. That's a file-system detail, not part of the interface spec.

There is no speed information stored on the card. The spec requires that the card work from DC to 25 MHz. If it works at 20 but not at 25, the problem is at your end.

GH

Yvan BOURNE wrote:

Reply to
ghelbig

Hi, OK, but what about the "33x", "80x", or even "133x" now ?

Yvan

Reply to
Yvan BOURNE

That's flash operation speed, not clock speed. And a marketing number, not a technical specification.

GH.

Reply to
ghelbig

133x corresponds to 20MB/s, which is accomplished by using the card in SD mode (4 pins) NOT in SPI mode (1 pin).

In the 4-pin SD mode, there are devices that can go form 0-25MHz, which tops out at around 12.6MB/s (something like 82x), and there are are some devices that can clock from 0-50MHz. The 133x parts are used in

4-pin mode and are clocking at something like 42MHz, give or take, from what I can tell.

Note that only SPI mode is free for everyone to use, but to use the card in 4-pin SD mode you have to be a member of the SD card group to get the spec.

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--Keith

Reply to
Keith

Hi, Thank you for your answers. My problem was (is...) the shape of the SPI signals. They are more signals sine than square signals :-( , even with a pull up. I have just a RTC and the SD card on SPI bus ; with short tracks on PCB.

Any suggestions ?

Yvan

Reply to
Yvan BOURNE

What processor? Processor IO voltages? What scope?

--Rocky

Reply to
Rocky

- FREESCALE 9S12

- All components in 3.3V

- Sort of datalogger

- "Bad" signals at Fclk = 12.5MHz

Yvan

Reply to
Yvan BOURNE

a) Are the signals from the SD card also rounded? b) Or are the signals in both directions rounded? If (b) is the case it could be a measurement problem. Apart from the pull-ups you don't have any other components on the SPI bus?

--Rocky

Reply to
Rocky

Also, have you looked at the errata for the SPI bus - I am not sure which exact silicon you are using, but there are quite a few errata relating to SPI. See

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--Rocky

Reply to
Rocky

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