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Topic: SD card became unrecognized by card readers (Read 12 times) previous topic - next topic

fat16lib

#25
Jan 18, 2012, 04:56 pm Last Edit: Jan 18, 2012, 05:06 pm by fat16lib Reason: 1
No mike, SD cards don't fail due to removal while powered on.  Billions have been made and people pull them from powered on devices all the time.

Look at the pins.  Power and ground are a bit longer than the signal pins so first the signal pins disconnect then power.

Here is the quote from the spec:
Quote

Hot Insertion
Support for hot insertion will be required on the host but will be supported through the
connector. Connector manufacturers will provide connectors that have power-pins long
enough to be powered before contact is made with the other pins. This approach is similar
to that used in PCMCIA and MMCA devices to allow for hot insertion.


The SD buffers the entire block internally before writing to flash.  It does the flash programming in a fail safe way.  It either completes correctly or the block is not marked as written if power fails.

Pulling a card can cause the file system to become corrupt but does not damage the card.

Grumpy_Mike

Yes but hot insertion is not the same as hot removal.
Anyway I am not sure if the card removed with the power on or the power was removed with it still being written to.

That is a scenario that is not duplicated by billions of people. It is very difficult to time that right in a piece of consumer equipment if you wanted to duplicate it. By constantly opening, writing and closing a file the chances of hitting a critical spot in the internal process increases dramatically. This is something that you would not expect to see in the field because that sort of cycling is not done in with consumer equipment.

I know you can kill flash memory by trying to write to it with lower than the required voltage. I used to design power detection circuits in set top boxes to file away channel information in the case of a power outage and I know if you didn't get it right you could damage the flash memory.

al_ra

you are right,

I didn't remove the SD card while running
I shut the power off during run - apparently it was worse

fat16lib

No!  Here is more detail.  Please read the Spec and manufacture's data sheets.  SD cards were designed to be foolproof.

Quote

Physical Layer Specification Version 3.00

6.1 Hot Insertion and Removal

To guarantee the proper sequence of card pin connection during hot insertion, the use of either a special hot-insertion capable card connector or an auto-detect loop on the host side (or some similar mechanism) is mandatory (Refer to the Mechanical Addenda).

No card shall be damaged by inserting or removing a card into the SD Memory Card bus even when the power (VDD) is up. Data transfer operations are protected by CRC codes, therefore any bit changes induced by card insertion and removal can be detected by the host.

The inserted card shall be properly reset also when CLK carries a clock frequency Each card shall have power protection to prevent card (and host) damage. Data transfer failures induced by removal/insertion are detected by the host. They should be corrected by the application, which may repeat the issued command.


Card connectors and cards conform to this spec.

fat16lib

Here is info from a typical datasheet for a SanDisk card:
Quote

Hot Insertion/Removal

Hot insertion and removal are allowed. The SanDisk SD Card will not be damaged by inserting or removing it into the SD bus even when the power is up:

• The inserted card will be properly reset also when CLK carries a clock frequency fPP.

• Data transfer failures induced by removal/insertion should be detected by the bus master using the CRC codes that suffix every bus transaction.

3.2.1. Power Protection

Cards can be inserted into or removed from the bus without damage. If one of the supply pins (VDD or VSS) is not connected properly, then the current is drawn through a data line to supply the card.

Data transfer operations are protected by CRC codes; therefore, any bit changes induced by card insertion and removal can be detected by the SD bus master. The inserted card must be properly reset also when CLK carries a clock frequency fpp. If the hot insertion feature is implemented in the host, than the host has to withstand a shortcut between VDD and VSS without damage.

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