I2C问题，求指教！ I2C bus error, SDA line low

发布于 2020-01-03 17:47:23 浏览：2993 订阅该版

* 本帖最后由 断崖独坐 于 2020-1-3 18:00 编辑 *

今天在用RTT写一个DS1307时钟芯片的程序，用的是GPIO模拟I2C，硬件为4.7K上拉5V
![1578044915(1).jpg](/uploads/202001/03/174938mfae0hrl2yfslr13.jpg)

下面为部分代码：

#define BSP_I2C1_SCL_PIN GET_PIN(B,6)  //i2c1 SCL
#define BSP_I2C1_SDA_PIN GET_PIN(B,7)  //i2c1 SDA

/* 获取ds1307 i2c1 */
static void ds1307_init(const char *name)
{
    /* 查找I2C总线设备，获取I2C总线设备句柄 */
    i2c_bus = (struct rt_i2c_bus_device *)rt_device_find(name);
    //i2c_bus = (struct rt_i2c_bus_device *) rt_i2c_bus_device_find(name);
        
    if (i2c_bus == RT_NULL)
    {
        rt_kprintf("can't find %s device!<br>", name);
    }
        initialized = RT_TRUE;
}

/* 写寄存器 */
static rt_err_t write_reg(struct rt_i2c_bus_device *bus, rt_uint8_t reg, rt_uint8_t data)//write_reg(i2c_bus, Address_second, data)
{
    rt_uint8_t buf[2]={0};
    struct rt_i2c_msg msgs;
                
    buf[0] = reg;
    buf[1] = data;
        
    msgs.addr = DS1307_ID;
    msgs.flags = RT_I2C_WR;
    msgs.buf = buf;
    msgs.len = 2;

/* 调用I2C设备接口传输数据 */
    if (rt_i2c_transfer(bus, &msgs, 1) == 1)
    {
        rt_kprintf("write_reg OK! <br>");
        return RT_EOK;
    }
    else
    {
        rt_kprintf("write_reg NO! <br>");
        return -RT_ERROR;
    }
}

开启了#define RT_I2C_BIT_DEBUG，提示I2C bus error, SDA line low，rt_i2c_transfer(bus, &msgs, 1)的返回值为-8， 如下图

![1578044314(1).jpg](/uploads/202001/03/174213q8m6e05lx5vqsd4q.jpg)

用示波器看，SDA为黄色，电平为3.3V
![5f5a174930a9349c0df52c9cd665a6e.jpg](/uploads/202001/03/174518mrprbtmtu6p8spor.jpg)
我单步仿真发现在初始化的时候，都默认为高电平时，SCL和SDA都为5V(下图中位置1)，但到了rt_i2c_transfer发送接收数据的时候，SDA的电平就只能到3.3V(下图中位置2)

![1578044181(1).jpg](/uploads/202001/03/174212trn40qszy4sm7tsb.jpg)

请问这是什么原因，在下比较小白，求指教！谢谢！

![1578044411(1).jpg](https://oss-club.rt-thread.org/uploads/202001/03/174212efl7kukff4pfrt5b.jpg)

15 个回答

红枫认证专家 2020-01-04

这家伙很懒，什么也没写！

红枫认证专家 2020-01-04

这家伙很懒，什么也没写！

红枫认证专家 2020-01-04

这家伙很懒，什么也没写！

红枫认证专家 2020-01-04

这家伙很懒，什么也没写！

断崖独坐 2020-01-05

这家伙很懒，什么也没写！

>就是地址右移1位(0x68>>1)

---

DS1307的地址是0x68啊，我有点不太明白，RTT这个I2C接口的设备ID，是发0x68，还是发D0或者D1了，这个个读和写的标志位msgs.flags是0和1吧，器件收到的是D0和D1吧，您帮我看下程序哪里有不对的，刚刚开始探索这个，谢谢！

typedef struct
{
    rt_uint8_t second;  //秒
    rt_uint8_t minute;  //分
    rt_uint8_t hour;    //时
    rt_uint8_t week;    //星期
    rt_uint8_t date;    //日
    rt_uint8_t month;   //月
    rt_uint8_t year;    //年
}Time_Typedef;
Time_Typedef TimeValue;  //定义时间缓存指针

#define DS1307_ID							0x68	//DS1307 器件地址
#define DS1307_Write						0xd0		//写 寄存器地址
#define DS1307_Read						0xd1		//读 寄存器地址
#define Address_second          0x00    //秒 寄存器地址
#define Address_minute          0x01    //分 寄存器地址
#define Address_hour            0x02    //时 寄存器地址
#define Address_week            0x03    //星期 寄存器地址
#define Address_date            0x04    //日 寄存器地址
#define Address_month           0x05    //月 寄存器地址
#define Address_year            0x06    //年 寄存器地址

/* 写寄存器 */
static rt_err_t write_reg(struct rt_i2c_bus_device *bus, rt_uint8_t reg, rt_uint8_t data)//write_reg(i2c_bus, Address_second, data)
{
    struct rt_i2c_msg msgs[2];
	
    msgs[0].addr = DS1307_ID;
    msgs[0].flags = RT_I2C_WR;
    msgs[0].buf = ®
    msgs[0].len = 1;
		
    msgs[1].addr = DS1307_ID;
    msgs[1].flags = RT_I2C_WR;
    msgs[1].buf = &data;
    msgs[1].len = 1;

/* 调用I2C设备接口传输数据 */
    if (rt_i2c_transfer(bus, msgs, 2) == 2)
    {
	rt_kprintf("write_reg OK!\r\n");
        return RT_EOK;
    }
    else
    {
        rt_kprintf("write_reg NO!\r\n");
	return -RT_ERROR;
    }
}

/* 读寄存器数据 */
rt_err_t read_regs(struct rt_i2c_bus_device *bus, rt_uint8_t reg, rt_uint8_t *buf) 
{
    struct rt_i2c_msg msgs[2];

msgs[0].addr = DS1307_ID;
    msgs[0].flags = RT_I2C_WR;
    msgs[0].buf = ®
    msgs[0].len = 1;

msgs[1].addr = DS1307_ID;
    msgs[1].flags = RT_I2C_RD;
    msgs[1].buf = buf;
    msgs[1].len = 1;
		
    /* 调用I2C设备接口传输数据 */
    if (rt_i2c_transfer(bus, msgs, 2) == 2)
    {
	rt_kprintf("read_regs OK!\r\n");
        return RT_EOK;
    }
    else
    {
	rt_kprintf("read_regs NO!\r\n");
        return -RT_ERROR;
    }
}

/* 修改时间 */
static void write_ymd_hms(void)
{
    rt_uint8_t wj_time=0;
   
		TimeValue.year = 20;
		TimeValue.month = 1;
		TimeValue.date = 2;
		TimeValue.hour = 13;
		TimeValue.minute = 55;
		TimeValue.second = 45;
	
    wj_time=HEX_BCD(TimeValue.year);
    write_reg(i2c_bus,Address_year,wj_time);   //年
				rt_thread_mdelay(1);
    wj_time=HEX_BCD(TimeValue.month);
    write_reg(i2c_bus,Address_month,wj_time);  //月
				rt_thread_mdelay(1);
    wj_time=HEX_BCD(TimeValue.date);
    write_reg(i2c_bus,Address_date,wj_time);   //日
				rt_thread_mdelay(1);
    wj_time=HEX_BCD(TimeValue.hour);
    write_reg(i2c_bus,Address_hour,wj_time);   //时
				rt_thread_mdelay(1);
    wj_time=HEX_BCD(TimeValue.minute);
    write_reg(i2c_bus,Address_minute,wj_time); //分
				rt_thread_mdelay(1);
    wj_time=HEX_BCD(TimeValue.second);
    write_reg(i2c_bus,Address_second,wj_time); //秒
				rt_thread_mdelay(1);
}

/* 读取时间 */
static void read_ymd_hms(void)
{
    rt_uint8_t wj_time=0;
		rt_uint8_t ret=0;
	
    read_regs(i2c_bus,Address_year,&wj_time);   //年
		TimeValue.year=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
    read_regs(i2c_bus,Address_month,&wj_time);  //月
		TimeValue.month=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
    read_regs(i2c_bus,Address_date,&wj_time);   //日
		TimeValue.date=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
    read_regs(i2c_bus,Address_hour,&wj_time);   //时
		TimeValue.hour=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
    read_regs(i2c_bus,Address_minute,&wj_time); //分
		TimeValue.minute=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
    read_regs(i2c_bus,Address_second,&wj_time); //秒
		TimeValue.second=BCD_HEX(wj_time);
				rt_thread_mdelay(1);
		if(TimeValue.hour>23)
		ret++;
		if(TimeValue.month>59)
			ret++;
		if(TimeValue.second>59)
			ret++;
		if(TimeValue.year>99)
			ret++;
		if((TimeValue.month>12)||(TimeValue.month==0))
			ret++;
		if((TimeValue.date>31)||(TimeValue.date==0))
			ret++;
		if (ret>0)
			rt_kprintf("read ds1307 err : %d\n", ret);

}