After the Data Ready (DR) has been set high a valid data packet is available in the RX data register. This
may be clocked out in RX mode or standby mode. After the data has been clocked out through the SPI the
Data Ready (DR) and Address Match (AM) pins are reset to low.
看上面这段话， DR 被置位，有效的数据包将在RX数据寄存器变为可用的， 数据时钟输出在RX模式和待机模式， 显然一开机DR将被置位
