when the chip is in receive mode. Likewise, TXis active when the chip is transmitting.The last four bits (3:0) in the status byte containsFIFO_BYTES_AVAILABLE. For readoperations (the R/W¯ bit in the header byte isset to 1), the FIFO_BYTES_AVAILABLE fieldcontains the number of bytes available forreading from the RX FIFO. For writeoperations (the R/W¯ bit in the header byte isset to 0), the FIFO_BYTES_AVAILABLE fieldcontains the number of bytes that can bewritten to the TX FIFO. WhenFIFO_BYTES_AVAILABLE=15, 15 or morebytes are available/free.