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10069 Datasheet(PDF) 20 Page - Texas Instruments |
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10069 Datasheet(HTML) 20 Page - Texas Instruments |
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20 / 50 page  CC2550 Preliminary Data Sheet (rev. 1.1) SWRS039 Page 20 of 51 Preamble bits (1010...1010) Data field Optional CRC-16 calculation Optionally FEC encoded/decoded 8 x n bits 16/32 bits 8 bits 8 bits 8 x n bits 16 bits Optional data whitening Legend: Inserted automatically in TX, processed and removed in RX. Optional user-provided fields processed in TX, processed but not removed in RX. Unprocessed user data (apart from FEC and/or whitening) Figure 8: Packet Format 20.3 Packet Handling in Transmit Mode The payload that is to be transmitted must be written into the TX FIFO. The first byte written must be the length byte when variable packet length is enabled. The length byte has a value equal to the payload of the packet (including the optional address byte). If fixed packet length is enabled, then the first byte written to the TX FIFO is interpreted as the destination address, if this feature is enabled in the device that receives the packet. The modulator will first send the programmed number of preamble bytes. If data is available in the TX FIFO, the modulator will send the two-byte (optionally 4-byte) sync word and then the payload in the TX FIFO. If CRC is enabled, the checksum is calculated over all the data pulled from the TX FIFO and the result is sent as two extra bytes at the end of the payload data. If whitening is enabled, the length byte, payload data and the two CRC bytes will be whitened. This is done before the optional FEC/Interleaver stage. Whitening is enabled by setting PKTCTRL0.WHITE_DATA=1. If FEC/Interleaving is enabled, the length byte, payload data and the two CRC bytes will be scrambled by the interleaver, and FEC encoded before being modulated. 21 Modulation Formats CC2550 supports amplitude, frequency and phase shift modulation formats. The desired modulation format is set in the MDMCFG2.MOD_FORMAT register. Optionally, the data stream can be Manchester coded by the modulator. This option is enabled by setting MDMCFG2.MANCHESTER_EN=1. Manchester encoding is not supported at the same time as using the FEC/Interleaver option. Manchester coding can be used with the 2-ary modulation formats (2-FSK, GFSK, OOK and MSK). 21.1 Frequency Shift Keying 2-FSK can optionally be shaped by a Gaussian filter with BT=1, producing a GFSK modulated signal. The frequency deviation is programmed with the DEVIATION_M and DEVIATION_E values in the DEVIATN register. The value has an exponent/mantissa form, and the resultant deviation is given by: E DEVIATION xosc dev M DEVIATION f f _ 17 2 ) _ 8 ( 2 ⋅ + ⋅ = The symbol encoding is shown in Table 17. Format Symbol Coding 2-FSK, GFSK ‘0’ – Deviation ‘1’ + Deviation Table 17: Symbol encoding for FSK modulation 21.2 Minimum Shift Keying When using MSK 1, the complete transmission (preamble, sync word and payload) will be MSK modulated. Phase shifts are performed with a constant transition time. This means that the rate of change for the 180-degree transition is twice that of the 90-degree transition. 1 Identical to offset QPSK with half-sine shaping (data coding may differ) |
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