分享使用串口操作DS18B20的代码，简化时序，提高系统实时性

2020-01-11 18:15发布

原理见帖子： https://www.amobbs.com/thread-5624824-1-1.html
从上次发帖子后，一值没有写这个代码，直到最近要用到18B20，才写了一个，测试成功
用硬件操作的好处是全程不需要禁止中断，另外还可以用串口中断方式或DMA来操作

硬件连接： DS18B20连接到STM32F407VE的PA0， PA0是UART4接口的TX脚，也是该串口单线半双工模式下时的TXRX脚，可以用此单引脚来发送和接收。该脚外接上拉电阻。

下面上代码：

static const unsigned char crc_tab[256]={
0, 94,188,226, 97, 63,221,131,194,156,126, 32,163,253, 31, 65,
157,195, 33,127,252,162, 64, 30, 95, 1,227,189, 62, 96,130,220,
35,125,159,193, 66, 28,254,160,225,191, 93, 3,128,222, 60, 98,
190,224, 2, 92,223,129, 99, 61,124, 34,192,158, 29, 67,161,255,
70, 24,250,164, 39,121,155,197,132,218, 56,102,229,187, 89, 7,
219,133,103, 57,186,228, 6, 88, 25, 71,165,251,120, 38,196,154,
101, 59,217,135, 4, 90,184,230,167,249, 27, 69,198,152,122, 36,
248,166, 68, 26,153,199, 37,123, 58,100,134,216, 91, 5,231,185,
140,210, 48,110,237,179, 81, 15, 78, 16,242,172, 47,113,147,205,
17, 79,173,243,112, 46,204,146,211,141,111, 49,178,236, 14, 80,
175,241, 19, 77,206,144,114, 44,109, 51,209,143, 12, 82,176,238,
50,108,142,208, 83, 13,239,177,240,174, 76, 18,145,207, 45,115,
202,148,118, 40,171,245, 23, 73, 8, 86,180,234,105, 55,213,139,
87, 9,235,181, 54,104,138,212,149,203, 41,119,244,170, 72, 22,
233,183, 85, 11,136,214, 52,106, 43,117,151,201, 74, 20,246,168,
116, 42,200,150, 21, 75,169,247,182,232, 10, 84,215,137,107, 53
};
unsigned char Check_crc8(unsigned char *p,unsigned char n)
{
unsigned char i,crc8=0;
for(i=0;i<n;i++)
crc8=crc_tab[crc8^p[i]]; //连续查表计算CRC
return crc8;
}
void DS18B20Init()
{
//时钟，UART4, PA0
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_UART4,ENABLE);
//GPIO->PA0
GPIO_InitTypeDef Gpio = {GPIO_Pin_0,GPIO_Mode_AF,GPIO_Low_Speed,GPIO_OType_OD,GPIO_PuPd_NOPULL};
GPIO_Init(GPIOA,&Gpio);
GPIO_PinAFConfig(GPIOA,GPIO_PinSource0,GPIO_AF_UART4);
//UART4
USART_InitTypeDef Uart = { 115200,
USART_WordLength_8b,
USART_StopBits_1,
USART_Parity_No,
USART_Mode_Rx|USART_Mode_Tx,
USART_HardwareFlowControl_None};
USART_Init(UART4,&Uart);
USART_HalfDuplexCmd(UART4,ENABLE);
USART_Cmd(UART4,ENABLE);
//
}
bool DS18B20Reset()
{
u8 rx;
UART4->BRR = 0x1117; //9600
UART4->DR = 0xF0;
while (!(UART4->SR&USART_SR_RXNE));
rx = UART4->DR;
UART4->BRR = 0x16C; //115200
return rx!=0xF0;
}
void DS18B20WriteByte(u8 byte)
{
for (int i=0;i<8;i++)
{
u8 c=(byte&0x01) ? 0xff:0x00;
UART4->DR = c;
byte>>=1;
while (!(UART4->SR&USART_SR_RXNE));
c=UART4->DR;
}
}
u8 DS18B20ReadByte()
{
u8 byte,rx;
for (int i=0;i<8;i++)
{
UART4->DR = 0xff;
byte>>=1;
while (!(UART4->SR&USART_SR_RXNE));
rx=UART4->DR;
if (rx==0xff) byte|=0x80;
}
return byte;
}
int DS18B20GetTemp()
{
u8 Buf[9];
//发送复位信号
if (!DS18B20Reset()) return -1;
//发送SKIP_ROM
DS18B20WriteByte(0xCC);
//发送转换温度命令
DS18B20WriteByte(0x44);
//等待转换, 最大750ms
OSTimeDly(800);
//发送复位信号
if (!DS18B20Reset()) return -1;
//发送SKIP_ROM
DS18B20WriteByte(0xCC);
//发送读取温度命令
DS18B20WriteByte(0xBE);
//读取9字节内存
for (int i=0;i<9;i++)
Buf[i]=DS18B20ReadByte();
//CRC
if (Check_crc8(Buf,9)!=0)
return -1;
return Buf[1]*256+Buf[0];
}