RdURXH0()，WrUTXH0()，找不到函数的原型，后来在寄存器定义里面看到了。如下：
#define rUTXH0 (*(volatile unsigned char *)0x1d00020)
#define rUTXH1 (*(volatile unsigned char *)0x1d04020)
#define rURXH0 (*(volatile unsigned char *)0x1d00024)
#define rURXH1 (*(volatile unsigned char *)0x1d04024)
#define WrUTXH0(ch) (*(volatile unsigned char *)0x1d00020)=(unsigned char)(ch)
#define WrUTXH1(ch) (*(volatile unsigned char *)0x1d04020)=(unsigned char)(ch)
#define RdURXH0() (*(volatile unsigned char *)0x1d00024)
#define RdURXH1() (*(volatile unsigned char *)0x1d04024)
#define UTXH0 (0x1d00020) //byte_access address by BDMA
#define UTXH1 (0x1d04020)
#define URXH0 (0x1d00024)
#define URXH1 (0x1d04024)
WrUTXH0('\r'),即把'\r'写到寄存器[0x1d00020]里面，而寄存器[0x50000027]是UART0的发送寄存器，也就是换行。而rUTXH0，也是UART的发送保持寄存器，若要做WrUTXH0('\r')相同的效果，则需把相应的命令值赋给rUTXH0：即：rUTXH0=“\r”。
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