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#1 2011-10-31 20:19:47

atrox
Contributor
Registered: 2010-01-08
Posts: 35

ISO15693 Glitches

I suspect, that changing the FPGA-Conf-Word produces glitches in the coil output. This glitches are between almost 0 and about 80uS and occur about 220us before a ISO15693 transmission (Reader->Tag). By chance this glitches sometimes look like a valid bit-time ans seem to confuse some VICCs (tags) - or at least they don't recover fast enough. 

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.
6101_6c61.png6114_6a51.png

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

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