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RFID Status Register

Tahir Mahmood
Expert 1250 points
Other Parts Discussed in Thread: TRF7970A

Hello,

I am writing to an inlay Tag from Texas instruments and I can sucsessfully write and read to many different tags.

One thing I observed is that I get A0 in the Status Register after sending the complete command to write single block no matter how much I wait to read the Status Register(except very small wait time then I get 80).

When I use another tag from Microsensys then I get E0 no matter how long I wait (except very small wait time) in the Status Register which has 8 Byte block with Option flag =0.

What should be value in the Status Register if the tag is written sucessfully or when no tag is found with write single block command.

With the Texas insturments inlay tag I observe A0 no matter tag is present or not while executing write single block command.But with the Microsensys tag I get A0 if no tag is present and E0 if the tag is present.

In all case I can sucessfully write to the tag with single write command.

Why one tag is giving A0 and the other E0 in the Status Register and why I always I get A0 with inlay Texas Instrument Tag no matter Tag is present or not.

Tahir 

  • 0
    TI__Mastermind 29105 points
    Hey Tahir,

    The status register doesn't really tell you if a tag is there or not. It also can't tell you if the tag was written correctly. It only gives the status or the TRF7970A. gyazo.com/cdc994c72e36d57ee55baacc1bc987a9

    After you transmit, you should get an IRQ with 0x80 indicating TX complete. This will happen whether there is a tag nearby or not.

    The 0xA0 you mentioned, means that you are getting a FIFO water mark interrupt, telling you that your FIFO is almost empty. This is expected operation. In most cases, this is fine, and can be ignored. If you were writing a large amount of data, then this interrupt would tell you to load more of that data into the FIFO.

    This interrupt can be disabled by the Interrupt Mask Register (0x0D) or the FIFO watermark can be adjusted in the "Adjustable FIFO IRQ Levels" register (0x14).

    Now, the 0xE0 you mentioned, is not as typical. This means that the tag has already started to respond before you serviced the IRQ status register. Do you have a large amount of latency in your system?

    Thanks,
    JD
  • 0 in reply to JD Crutchfield
    Expert 1250 points
    I am not looking for the Interrupt but I just wait for fixed amount of time 40 ms and then check the Status Register. I only want to check the B6 bit of status register to see that the TAG has started sending data back (RX start)or not. Which tells me that tag is present and responding when I try to write into it.Why the Texas inlay tag does not set B6 to signal RX start while other two different companies tags set B6.
  • 0 in reply to Tahir Mahmood
    TI__Guru*** 135355 points

    Hi Tahir,

    When using the Write Single Block command with TI inlays, you will need to set the Option flag in your request flags (B6) in order for the tag to accept the command. In order to  get a reply from any ISO15693 tag when using the Option flag, you will need to send out an End Of Frame (EOF) after you finish transmitting the command. This should be done once you receive the TX Complete. At that time you can send a Transmit Next Time Slot (0x14) direct command to the TRF7970A in order to have it issue the EOF marker. Then the tag will reply and you can handle that normally.

    The data sheets for the TI Standard, Pro, and Plus transponders will list all commands which require this usage of the Option flag.

  • 0 in reply to Ralph Jacobi
    Expert 1250 points

    One of the Evaluation boards is using the crystal 9C-13.560MAAJ-T and the other is using 7A-13.560MAAJ-T with TRF7970A.Is there any difference between the working performace or EMC between the two crystals?

  • 0 in reply to Tahir Mahmood
    TI__Mastermind 44060 points

    Hi Tahir,

    The 9C-13.560MAAJ-T which was used on the EVM board has been taken through FCC part 15 intentional radiator compliance testing and passed without problems.  On the eZ430 board, which uses the 7A-13.560MAAJ-T, this board was not taken through FCC testing.  I would still expect it would pass, but this board was a reference design only with only a minimal number of boards produced. 

    If you do need a smaller form factor crystal, you could also look at the Epson Q24FA20H00396, which was used on the TRF7970ATB board.  This board was also tested for FCC compliance. 

    http://www.ti.com/tool/TIDM-NFC-TRANSCEIVER