STM32F103驱动W5500程序的问题

我用STM32驱动W5500成功了，不过成立有个地方不明白，想请教大家。

unsigned char Read_W5500_1Byte(unsigned short reg)

{

unsigned char i;

GPIO_ResetBits(W5500_SCS_PORT, W5500_SCS);//ÖÃW5500µÄSCSΪµÍµçƽ

SPI1_Send_Short(reg);//ͨ¹ýSPI1д16λ¼Ä´æÆ÷µØÖ·

SPI1_Send_Byte(FDM1|RWB_READ|COMMON_R);//ͨ¹ýSPI1д¿ØÖÆ×Ö½Ú,1¸ö×Ö½ÚÊý¾Ý³¤¶È,¶ÁÊý¾Ý,Ñ¡ÔñͨÓüĴæÆ÷

i=SPI_I2S_ReceiveData(SPI1);

SPI1_Send_Byte(0x00);//·¢ËÍÒ»¸öÑÆÊý¾Ý

i=SPI_I2S_ReceiveData(SPI1);//¶ÁÈ¡1¸ö×Ö½ÚÊý¾Ý

GPIO_SetBits(W5500_SCS_PORT, W5500_SCS);//ÖÃW5500µÄSCSΪ¸ßµçƽ

return i;//·µ»Ø¶ÁÈ¡µ½µÄ¼Ä´æÆ÷Êý¾Ý

}

请问粗体斜体的那句有什么作用？我看不懂，请指教，谢谢！