There are several modes to use when receiving data. If the FIFO is used, then there must be a preamble and sync word added to the transmitted data. If the packet handler is enabled, the header bytes and the packet length fields are included in the packet and it is controlled by the registers of the peripheral while the CRC checks the integrity of the data. If packet handling is disabled then the header bytes, packet length and CRC become part of the data transfer and must be maintained by the CPU when writing the data to the FIFO.