RFID design

Go To Last Post
3 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi there,
I am on the design state of an RFID tag reader using the HTRC110 philips chip and an ATtiny2313 in order to read 64 bit, 125KHz read only tags.
I have a serious problem that sometimes I can read the tag's data but sometimes I cannot (using the same tag and without change the PIC's code). I found that sometimes the incomind data bits are unfortunately inverted.
Does anybody hava any idea or information about it???

Thanks a lot.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

If it's a manchester code, the information is in the transitions not the absolute polarity, so the same manchester datastream should produce the same data whether inverted or not. If the decoder is making assumptions about polarity, or getting out of sync, inverted data can be the result.
One possible answer if you are getting either correct data or inverted data, is if you get a CRC error, try inverting the data and checking again.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Because of this invertionn I decided to use 2 different routines in my code. First I check the data as non-inverted and I check the CRC. If the CRC is Ok then the data is valid. If the CRC is not Ok I invert the logic using the 2nd routine and I read the data again, then I check again the CRC. If the CRC is Ok then the data is valid.
There is no problem of reading the data, but I can't understand the reason of this problem. Maybe the rf field is not tuned well and the chip read the data with a phase and then it gives me the data shifted 180 degrees. I realy don't know.

Do you have any idea???

Thanks a lot.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer