On Jul 28, 11:52 am, "
wrote:
On Jul 26, 5:37 pm, wrote: On 25 Jul, 21:43, Chris wrote:

Of course they can - incorrect data downloaded to cards can easily
makethem inoperable.

I've not yet come across r/w memory that can't be reset if theres
dodgy data on it so unless they're upgrading any software there may be
on it I can't see how it could happen. And if thats the case you have
to ask yourself why.

To followup:
Just found this 2K (256x8) eeprom

http://www.atmel.com/atmel/acrobat/doc0958.pdf

Has a permanent software write protection for the first half of the
memory.

"Write Protection
The software write protection, once enabled, permanently write
protects only the first-half of the array ...

The software write protection cannot be reversed even if the device is
powered down."

I've only skimmed that data sheet but it looks like if you send a
write command with a device address of 0110 instead of 1010 then
you'll set this bit.

You really don't want to send a software update to your readers that
drops a byte from the command being sent to the chip - most cards will
just fail to work, but a few will get that magic 0110 bit pattern at
the wrong point and will then be permanently broken.

Tim.