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CR14 Datasheet(PDF) 30 Page - STMicroelectronics |
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CR14 Datasheet(HTML) 30 Page - STMicroelectronics |
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30 / 46 page  6 CR14 ISO14443 type-B Radio Frequency data transfer CR14 30/46 6.9 Transmission Frame The Request Frame transmission must be followed by a minimum delay, t0 (see Table 13), in which no ASK or BPSK modulation occurs, before the Answer Frame can be transmitted. t0 is the minimum time required by the CR14 to switch from transmission mode to reception mode, and should be inserted after each frame. After t0, the 13.56MHz carrier frequency is modulated by the PICC at 847kHz for a minimum time of t1 (see Table 13) to allow the CR14 to synchronize. After t1, the first phase transition generated by the PICC represents the start bit (‘0’) of the Answer SOF (or the start bit ‘0’ of the first data character in non SOF/EOF mode). Figure 26. Example of a Complete Transmission Frame 6.10 CRC The 16-bit CRC used by the CR14 follows the ISO14443 type B recommendation. For further information, please see Appendix A on page 44. The two CRC Bytes are present in all Request and Answer Frames, just before the EOF. The CRC is calculated on all the Bytes between the SOF and the CRC Bytes. Upon transmission of a Request from the CR14, the PICC verifies that the CRC value is valid. If it is invalid, it discards the frame and does not answer the CR14. Upon reception of an Answer from the PICC, the CR14 verifies that the CRC value is valid. If it is invalid, it stores the value FFh in the Input/Output Frame Register. The CRC is transmitted Least Significant Byte first. Each Byte is transmitted Least Significant Bit first. Figure 27. CRC Transmission Rules SOF Cmd Data CRC CRC EOF 12 bits at 106Kb/s 10 bits 10 bits 10 bits 10 bits 10 bits Sent by the CR14 t0 64/fs Min t1 80/fs Min Sync fs = 847.5kHz SOF Data CRC CRC EOF 12 or 13 bits 10 bits 12 or 13 bits 10 bits 10 bits tWDG Case of Answer Frame with SOF & EOF Sent by the PICC Sync Data Data CRC tWDG Case of Answer Frame without SOF & EOF Data CRC t0 64/fs Min t1 80/fs Min 10 bits 10 bits 10 bits 10 bits 10 bits Output Data Transfer using ASK Modulation Input Data Transfer using 847kHz BPSK Modulation ai12052 tDR LSByte MSByte CRC 16 (8 bits) CRC 16 (8 bits) LSBit MSBit LSBit MSBit ai09256 |
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