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Diffstat (limited to 'firmware/doc/bitpattern.txt')
| -rw-r--r-- | firmware/doc/bitpattern.txt | 102 |
1 files changed, 0 insertions, 102 deletions
diff --git a/firmware/doc/bitpattern.txt b/firmware/doc/bitpattern.txt deleted file mode 100644 index 2594a4c..0000000 --- a/firmware/doc/bitpattern.txt +++ /dev/null @@ -1,102 +0,0 @@ -DATA CODING - -ISO 14443 A bit patterns PCD -> PICC direction: - -Sequence X After time of 64/fC a "pause" shall occur -Sequence Y for the full bit duration (128/fC) no modulation shall occur -Sequence Z at the beginning of the bit duration a pause shall occur - - -logic 1 Sequence X -logic 0 Sequence Y with two exceptions: - - if there are two or more contiguous '0, Z used from the second on - - if the first bit after SOF is 0, sequence Z used for all contig. 0's -SOF Sequence Z -EOF Logic 0 followed by Sequence Y -No Inform At least two sequences Y - - - -FRAME TYPES - -During anti collision we have two frame types: - -1) REQA/WUPA (short frame) - -Short frame is seven bits with SOF/EOF "SOF 0 1 2 3 4 5 6 EOF" - -REQA 0x26 S 0101010 E Z ZXYXYXY ZY -WUPA 0x52 S 0100101 E Z ZXYZXYX YY -REQA_t 0x35 S 1001110 E Z XYZXXXY ZY - -2) ANTICOL/SELET (standard frame) - -Standard frame: minimum "SOF byte parity EOF", e.g. - - S 01234567 P 01234567 P 01234567 P E - -Anticol frame: like standard frame, but - - frame splitted between PCD and PICC - - total bit length is 56 - - length of PCD part: 16 data bits to 55 data bits - - length of PICC part: 1 data bit to 40 data bits - - split can occur at any bit position - - full byte: split after complete byte: Parity added after last PCD bit - - split byte: No Parity is added after last PCD bit - - each half of the split frame has its own SOF / EOF - -BIT TIMING - -One bit clock is fC/128, i.e. 105937.5 kHz, resulting in 9.43uS bit time - -The "pause" has to be min. 2uS, or 21.2% of the bit duration. - - -SAMPLING - -Given the pause is only 21.2%, four samples per bit clock are not really enough -to catch the pause under all circumstances. - -Given four-times and eight-times oversampling, we get: - - 4-over 8-over -Sequence X 0010 00001000 (00000100) -Sequence Y 0000 00000000 -Sequence Z 1000 10000000 (01000000) - - - -Ideas: -- if we ignore final 'Y' sequence, DATLEN is 32 (8 clocks, four bits each), therefore - we can just configure SSC to sample one frame of 32 sample bits after the start condition - was met. - - -SAMPLING DURING STANDARD FRAMES - -The maxiumum frame size is 256 data bytes. We have to add two bytes CRC (=258 -bytes), plus parity (2064bits, plus 258 bits parity, equals 2322 data bits. Add -SOF / EOF with three bit clocks, and we have 2325 total data bits for a -maximum-sized frame. At four-times oversampling, this is 9300 sampled bits, -equals to 1162.5 bytes (eight-times oversampling consequently 2325 bytes). - - - -BIT SYNCHRONOUS RESPONSE IN SPLIT FRAME - -For some stupid reasons, the frame delay time for synchronous frames is not in -relation to the bit clock but in relation to the last rising edge of a -modulation pause. - -Therefore we need some trickery. Every rising edge resets TC2 of the SAM7, which -is clocked by the carrier clock. Once RA compare is true, TIOA2 will see a -rising edge, which is connected to TF, the SSC Tx Framer. - -On The Tx side we have to run the SSC always at 847.5kHz - - - - -thoughts: -falling edge of demodulated signal: counter reset, TIOB set -RB Compare: TIOB reset |