- if (Uart.highCnt < 7) { // wait for a stable unmodulated signal
- if (Uart.twoBits == 0xffff) {
- Uart.highCnt++;
- } else {
- Uart.highCnt = 0;
- }
- } else {
- Uart.syncBit = 0xFFFF; // not set
- // look for 00xx1111 (the start bit)
- if ((Uart.twoBits & 0x6780) == 0x0780) Uart.syncBit = 7;
- else if ((Uart.twoBits & 0x33C0) == 0x03C0) Uart.syncBit = 6;
- else if ((Uart.twoBits & 0x19E0) == 0x01E0) Uart.syncBit = 5;
- else if ((Uart.twoBits & 0x0CF0) == 0x00F0) Uart.syncBit = 4;
- else if ((Uart.twoBits & 0x0678) == 0x0078) Uart.syncBit = 3;
- else if ((Uart.twoBits & 0x033C) == 0x003C) Uart.syncBit = 2;
- else if ((Uart.twoBits & 0x019E) == 0x001E) Uart.syncBit = 1;
- else if ((Uart.twoBits & 0x00CF) == 0x000F) Uart.syncBit = 0;
- if (Uart.syncBit != 0xFFFF) {
- Uart.startTime = non_real_time?non_real_time:(GetCountSspClk() & 0xfffffff8);
- Uart.startTime -= Uart.syncBit;
- Uart.endTime = Uart.startTime;
- Uart.state = STATE_START_OF_COMMUNICATION;
- }
+ Uart.syncBit = 9999; // not set
+ // we look for a ...xxxx1111111100x11111xxxxxx pattern
+ // (unmodulated, followed by the start bit = 8 '1's followed by 2 '0's, eventually followed by another '0', followed by 5 '1's)
+#define ISO14443A_STARTBIT_MASK 0x007FEF80 // mask is 00000000 01111111 11101111 10000000
+#define ISO14443A_STARTBIT_PATTERN 0x007F8F80 // pattern is 00000000 01111111 10001111 10000000
+ if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 0 == ISO14443A_STARTBIT_PATTERN >> 0) Uart.syncBit = 7;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 1 == ISO14443A_STARTBIT_PATTERN >> 1) Uart.syncBit = 6;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 2 == ISO14443A_STARTBIT_PATTERN >> 2) Uart.syncBit = 5;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 3 == ISO14443A_STARTBIT_PATTERN >> 3) Uart.syncBit = 4;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 4 == ISO14443A_STARTBIT_PATTERN >> 4) Uart.syncBit = 3;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 5 == ISO14443A_STARTBIT_PATTERN >> 5) Uart.syncBit = 2;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 6 == ISO14443A_STARTBIT_PATTERN >> 6) Uart.syncBit = 1;
+ else if ((Uart.fourBits & ISO14443A_STARTBIT_MASK) >> 7 == ISO14443A_STARTBIT_PATTERN >> 7) Uart.syncBit = 0;
+ if (Uart.syncBit != 9999) { // found a sync bit
+ Uart.startTime = non_real_time?non_real_time:(GetCountSspClk() & 0xfffffff8);
+ Uart.startTime -= Uart.syncBit;
+ Uart.endTime = Uart.startTime;
+ Uart.state = STATE_START_OF_COMMUNICATION;