NFC Digital Protocol - CWI

NFC-B Technology5.3 Frame FormatTo transmit data, the NFC Forum Device configured for NFC-B Technology uses frames that arebuilt from characters. This section defines the format of characters and frames.A character consists of a Logic “0” start bit, a Logic “1” stop bit and eight data bits. The stop bit,start bit, and each data bit has a length of one bit duration (bd**). Figure 15 shows the characterformat.Poll and Listen ModeStart lsb msb Stopb1 b2 b3 b4 b5 b6 b7 b810 bdFigure 15: NFC-B – Character FormatRequirements 43: Character Format – NFC-B Technology5.3.1.1 A character MUST consist of a start bit (Logic “0”), 8 data bits, and a stop bit (Logic“1”). The stop bit, start bit, and each data bit MUST be one bit duration (bd).Characters are sent as frames, as shown in Figure 16.n x (start bit + 8 data bits + stop bit)StartBitb1 b2 b3 b4 b5 b6 b7 b8StopBitStartBitb1 b2 b3 b4 b5 b6 b7 b8StopBit...StartBitb1 b2 b3 b4 b5 b6 b7 b8StopBit1 st byte2 nd byte n th byteFigure 16: NFC-B – Frame FormatRequirements 44: Frame Format – NFC-B TechnologyPoll and Listen Mode5.3.1.2 A frame MUST consist of characters that are aligned as shown in Figure 16.NOTEThe frame format defined in Figure 16 deviates from [ISO/IEC_14443]. SoF andEoF as defined in [ISO/IEC_14443] are defined by this specification as SoS and EoSat the sequence layer.5.4 Data and Payload FormatData transmitted in an NFC-B frame have the following substructure. They consist of the payloadand of an EoD (SoD is not used).The payload consists of the Commands and Responses described in Section 5.5.The EoD contains a 2-byte checksum referred to as CRC_B. The CRC_B is a function of k databits, which is a multiple of 8. Input for CRC_B calculation is the payload.Figure 17 illustrates the NFC-B data and payload format.NFC Digital Protocol Page 51