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#1 2009-01-23 16:57:07

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

Can't read 14443 card - suspect hardware

Hello all-

first post and I'm still learning, so please bear with me...

I have a PM3 working as a reader on LF, but can't get HF to work.  I've made an antenna resonant at 13.56 MHz and the tune command returns HF: 52 mA / 12360 mV, so I assume there is enough energy to read the card.  However, I don't see any change in the readout when doing a 'hi_read' with or without a card.  Has anyone ever run into anything like this?  I found some wrong component values installed and missing parts after receiving the board, so I am a little suspect of the build. 

Any ideas or ways I could troubleshoot this??

Thx in advance-

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#2 2009-01-27 17:46:52

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

Re: Can't read 14443 card - suspect hardware

...still having problems...

One thing I noticed was the ASK modulation index was around 45% when trying to read a 14443B card using 'hi14read'.  ISO spec is 10%, so maybe the card is not staying powered during the read? 

My PM3 is built with R45,R46 = 10k, and R22,R27,R28,R29 = 33 ohms, is this the same as other PM3s out there?

Anyone measured peak-to-peak voltage on their antenna coil w/ a scope for a working setup?  That would remove the uncertainty of the 'tune' commands impedance settitng.  If so, I'd love to know what others are getting.

thanks-

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#3 2009-02-02 14:30:09

henrym97
Contributor
From: North America
Registered: 2009-01-23
Posts: 18

Re: Can't read 14443 card - suspect hardware

Finally figured this one out! Not a hardware problem at all!

In the iso14443 function the REQB message is built in an array: cmd[] = [0x05 0x00 ...];.  For some reason the array was being overwritten with different values at compile time (still not sure why).  The only way to get it to work was by explicit static assignement of each byte: cmd[1] = 0x05; cmd[2] = 0x00; etc. 

During this debug we also found the CRC was being calculated incorrectly.  Even though the code was exactly the same as in the 14443-3 spec, it computed wrong values.  This was strange since no one else has seemed to have this problem.  Again, it seemed to be the compiler, since after sperating out the initial XOR, the CRC started to return the correct value.

After making these changes, the card responded.   Now on to the next set of problems...

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