串行外设接口（SPI）fpga 被动接收,在下降沿 采集数据并发送数据 1BYTE,要求mcu在末端采集数据。并在下降沿之前准备好数据。-Serial Peripheral Interface (SPI), The fpga passive receiving, at the falling edge of data collection the send data 1BYTE, mcu data collected at the end. And the data ready before the falling edge.