You can snoop iso15693 supported communication with "hf iclass snoop" command no more things to explain; try to test/read forum/documentation before posting.
]]>The standard 128 samples were not enough.
With "data samples 2000" it worked (got the UID with the CRC).
The demodulator currently used is a correlation type demodulator. This means, over the incoming samples a correlation value for each symbol is calculated. The symbol with the highest value "wins" - i.e. is returned as the decoded symbol.
The three symbols the code looks for is "logic 1", "logic 0" and "End of Frame".
This type of demodulator is usually quite robust, also in low SNR conditions - since it decides for the symbol with likelihood.
Here lays the problem for collision detection: In an multi-card environment one card will produce a slightly stronger signal than the other(s), e.g. because its slightly nearer than the other one(s). The correlation demodulator will always decodes the strongest signal, even if it is only slightly stronger.
The only solution I could think of at the moment is to introduce a fourth symbol, which is a mixture of logic-0 and logic-1. Is this feasible? Won't it hurt the detection performance in bad SNR conditions, as it is similar to the other both bit symbols?
]]>I've included two scope traces. They both show the signal on the rectified receiver coil. The transmission (SOF, read-command, etc.. in 2of4-mode) starts at the center line.
I suspect line 250 in armsrc/iso15693.c:
FpgaWriteConfWord(FPGA_MAJOR_MODE_HF_READER_TX);
Questions:
a) can I read the ConfWord, and set it only when needed different?
b) at the moment the FPGA is set to FPGA_MAJOR_MODE_HF_READER_RX_XCORR when in receive or idle-but-coil-energized mode.
Can I instead put the FPGA in HF_READER_TX when idle (mean, when I don't send data via AT91C_BASE_SSC->SSC_THR ?)
This way the glitch will happen somewhere else - long before the read command is send.
thanks
]]>As it happens to be, this card is a Texas Instruments "Tag-it™ HF" 1st generation card which is NOT ISO15693 compatible.
To be more specific:
"The first 13.56 MHz transponder developed by Texas Instruments was the Tag-It HF. This
transponder was part of the technical development that went into the ISO 15693 standard.
However, the original Tag-It HF transponders are not ISO compatible (whereas their
successors, the Tag-It HF-I are ISO compatible – please note the small but significant
difference!). They are still being produced in great numbers and have an installed base of many
millions worldwide. The transponders use a proprietary communication interface of Texas
Instruments."
source: www.metratec.com/fileadmin/docs/en/howtos/metraTec_Programming_Guide.pdf
So, going back to my problem:
does anyone know where I can find a reader (with RS232 or USB connection) which is able to read "Tag-it™ HF" tags?
]]>IIRC the dual subcarrier should gracefully degrade to single subcarrier on the receiver side, if you correctly filter out the single subcarrier that you support. (It's been some time since I looked into 15693, so I might be wrong.)
I agree, that should work. But as far as I understand, a full dual-carrier implementation should make transmissions more robust than single subcarrier... ?
I've tried the current signal processing implementation in the iso15693.c with dual carrier transmissions and it does not cope very well. In fact, the error rate is so high you need quite luck to read something. If we like to filter a subcarrier, the ideal place for that would be the FPGA, wouldn't it ?
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