14.3.1.1.1 Synchronization Header (SHR)

The SHR consists of a four-octet preamble field (all zero), followed by a single byte start-of-frame delimiter (SFD) which has the predefined value 0xA7. During transmission, the SHR is automatically generated by the AT86RF212B, thus the Frame Buffer shall contain PHR and PSDU only.

The transmission of the SHR requires 40 symbols for a transmission with BPSK modulation and 10 symbols for a transmission with O-QPSK modulation. The SHR duration depending on the selected data rate is illustrated in the Timing Summary.

The fact that the SPI data rate is normally higher than over-the-air data rate, allows the microcontroller to first initiate a frame transmission and then as the SHR is transmitted write the frame data. This is to minimize frame buffer data fill overhead transmission delay.

During a frame reception, the SHR is used for synchronization purposes. The matching SFD determines the beginning of the PHR and the following PSDU payload data.