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054-beta does not support ASKRAW and manchester

Hi,

thanks a lot for the great rfidler.

We are trying to read from an EM4450 tag. According to the datasheet this tag uses ASK and manchester encoding.
When setting these parameters the reader function does not work and the board turns the error led on.
*> set tag askraw
OK

*ASKRAW> set manchester on
OK

*ASKRAW> reader


Without the manchester encoding the board works ok, but of course the encoding is wrong:
*ASKRAW> set tag askraw
OK

*ASKRAW> set manchester off
OK

*ASKRAW> reader
1C4F155555555555555555555554313C555555555555555555555550C4F15555
AAAAAAAA86239AAAAAAAAAAAAAAAAAAAAAAA388E2AAAAAAAAAAAAAAAAAAAAAA8
55555555555555554311C555555555555555555555550C471555555555555555
18AAAAAAAAAAAAAAAAAAAAAAA189E2AAAAAAAAAAAAAAAAAAAAAA86238AAAAAAA

Any ideas?

F
Tagged:

Comments

  • We just confirmed this still to be the case running firmware 056-beta.
  • Converting a portion of the raw hex to binary:

    ASKRAW> hextobin AAAA86239                                                    
    101010101010101010000110001000111001

    We can see that there are manchester encoding errors - sequences of 3 or more '0'

    I have a ski pass that is bassed on an EM4x50 (not sure exactly which model), and I see the same thing.

    I suspect that you've got another layer of modulation going on here - some guard periods etc. surrounding the valid data. With this type of tag you normally need to implement some more direct reading/writing capability - see Q5 for an example. There will be a command structure for reading specific blocks instead of just picking up the raw stream...

    It may also be possible to extract the right bit of the data by switching manchester off, looking for a specific pattern which represents the gap and then manchester decoding the following n bits...



  • And I've just looked at the datasheet:

    Standard Read Mode
    After a Power-On-Reset and upon completion of a command, the chip will execute the Standard Read Mode, in which it will
    send data continuously, word by word from the memory section defined between the First Word Read (FWR) and Last
    Word Read (LWR). When the last word is output, the chip will continue with the first word until the transceiver sends a
    request. If FWR and LWR are the same, the same word will be sent repetitively. The Listen Window (LIW) is generated
    before each word to check if the transceiver is sending data. The LIW has a duration of 320 (160 opt 32) periods of the RF
    field. FWR and LWR have to be programmed as valid addresses (FWR ≤ LWR and ≤ 33).

    There's a graphic on page 6 which shows the LIW insterted into the bitstream - this would appear as sequences of '0', so I guess what you're seeing is the LIW.

    image
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