C8051f系列单片机是一种高速，集成度很高的单片机，功能还是蛮强大的。我在用此款单片机读取ST 公司的三轴加速度计的时候发现输出总是全1。于是，我用keil c的单步调试功能。一步一步调试，于是我发现执行到一条把某一管脚置1的语句之后，watch窗口显示的相应管教状态仍是0.

于是我觉得可能是硬件的问题，引脚一直接地被拉低。果然，我在查看电路板的线路时发现sdi和sdo两根线与另外两个引脚相连，而这个连接是我修改版图时无意连接上的。而且一个引脚被配置成高电平，另外一个被配置成低电平。所以sdi和sdo都一直保持低电平和高电平。所以不能对传感器进行正常的配置和读取数据。

另附lis3lv02dq读取程序，采用的是虚拟spi总线。

#include "main.H"

unsigned char spi_comm(unsigned char outgoing_byte)

{

    uchar incoming_byte, x;

    acc_spc = 1; //Pull SPI clock high

    for(x = 0 ; x < 8 ; x++)

    {

    if(outgoing_byte&0x80)

          acc_sdi =1; //Put bit on SPI data bus

    else acc_sdi = 0;

          outgoing_byte <<= 1; //Rotate byte 1 to the left

        acc_spc = 0; //Toggle the SPI clock

        acc_spc = 1;

        incoming_byte <<= 1; //Rotate byte 1 to the left

if(acc_sdo)    //Read bit on SPI data bus

       incoming_byte += 0x01;        

    }

    return(incoming_byte);

}

unsigned char read_register(unsigned char register_name)

{

    uchar in_byte;

    register_name |= 0x80; //Set D7 to 1 for read mode

   acc_cs = 0; //Select LIS

    in_byte = spi_comm(register_name); //SPI read 6-bit register from LIS

    //printf("In1 = %h ", in_byte);

    //in_byte is nothing, we need to clock in another 8 bits

    in_byte = spi_comm(0x00); //Send nothing, but we should get back the register value

    acc_cs = 1;

    return(in_byte);

}

//Sends a write command to LIS

void write_register(unsigned char register_name, unsigned char register_value)

{

    unsigned char in_byte;

    register_name &= 0x7f; //Clear D7 to 0 for write mode

    acc_cs = 0; //Select LIS

    in_byte = spi_comm(register_name); //SPI read 6-bit register from LIS

    //printf("In1 = %h ", in_byte);

    //in_byte is nothing, we need to clock in the value to write

    in_byte = spi_comm(register_value); //Send nothing, but we should get back the register value

    acc_cs = 1;

    //Return nothing

}

 void acc_spi(void)

  {

    acc_cs = 1; //Unselect LIS

   // CK = 0;

  // acc[0] = read_register(0x0F); //Read register WHO_AM_I   

    write_register(0x20,0xc7); //Power on device, enable all axis, and turn off self test - CTRL_REG1

    delay(5); 

write_register(0x21,0x44);

while(!acc_rdy);     

    acc[1] = read_register(0x28); //Read outx_l

    acc[0] = read_register(0x29); //Read outx_h

acc[3] = read_register(0x2a);

acc[2] = read_register(0x2b);

acc[5] = read_register(0x2c);

acc[4] = read_register(0x2d);

    }