UART实验心得

今天做了UART的实验。一开始一直不理解程序开始的

 GPHCON |= 0xa0; //GPH2,GPH3 used as TXD0,RXD0
 GPHUP = 0x0c; //GPH2,GPH3禁止内部上拉
这两句。

void init_uart( )
{//初始化UART

    GPHCON |= 0xa0;        //GPH2,GPH3 used as TXD0,RXD0

    GPHUP     = 0x0c;        //GPH2,GPH3禁止内部上拉


    ULCON0     = 0x03;        //8N1    

    UCON0     = 0x05;        //查询方式

    UFCON0 = 0x00;        //不使用FIFO

    UMCON0 = 0x00;        //不使用流控

    UBRDIV0 = 12;        //波特率为57600


}

后来查看S3C2410X的手册

GPH4 [9:8] 00 = Input 01 = Output
           10 = TXD1 11 = Reserved
GPH3 [7:6] 00 = Input 01 = Output
           10 = RXD0 11 = reserved
GPH2 [5:4] 00 = Input 01 = Output
           10 = TXD0 11 = Reserved
GPH1 [3:2] 00 = Input 01 = Output
           10 = nRTS0 11 = Reserved
GPH0 [1:0] 00 = Input 01 = Output
           10 = nCTS0 11 = Reserved

才知道这么回事。

另外代码

void putc(unsigned char c)
{
    while( ! (UTRSTAT0 & TXD0READY) );
    UTXH0 = c;
}

unsigned char getc( )
{
    while( ! (UTRSTAT0 & RXD0READY) );
    return URXH0;
}

也可以参看手册一下内容

UTRSTATn	Bit	Description	Initial State
Transmitter empty	2	Set to 1 automatically when the transmit buffer register has no valid data to transmit and the transmit shift register is empty. 0 = Not empty 1 = Transmitter (transmit buffer & shifter register) empty	1
Transmit buffer empty	1	Set to 1 automatically when transmit buffer register is empty. 0 =The buffer register is not empty 1 = Empty (In Non-FIFO mode, Interrupt or DMA is requested. In FIFO mode, Interrupt or DMA is requested, when Tx FIFO Trigger Level is set to 00 (Empty)) If the UART uses the FIFO, users should check Tx FIFO Count bits and Tx FIFO Full bit in the UFSTAT register instead of this bit.	1
Receive buffer data ready	0	Set to 1 automatically whenever receive buffer register contains valid data, received over the RXDn port. 0 = Empty 1 = The buffer register has a received data (In Non-FIFO mode, Interrupt or DMA is requested) If the UART uses the FIFO, users should check Rx FIFO Count bits and Rx FIFO Full bit in the UFSTAT register instead of this bit.	0