I2C 总线精要

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== 概述 ==
 
== 概述 ==
  
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两根线： SDA， SCL
  
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<br><br>
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== 软件实现 ==
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<source lang=cpp>
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#define SCL    TRISB4 // I2C bus
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#define SDA    TRISB1 //
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#define SCL_IN  RB4    //
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#define SDA_IN  RB1    //
 +
 +
To initialize the ports set the output resisters to 0 and the tristate registers to 1 which disables the outputs and allows them to be pulled high by the resistors.
 +
SDA = SCL = 1;
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SCL_IN = SDA_IN = 0;
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 +
We use a small delay routine between SDA and SCL changes to give a clear sequence on the I2C bus. This is nothing more than a subroutine call and return.
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void i2c_dly(void)
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{
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}
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The following 4 functions provide the primitive start, stop, read and write sequences. All I2C transactions can be built up from these.
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void i2c_start(void)
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{
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  SDA = 1;            // i2c start bit sequence
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  i2c_dly();
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  SCL = 1;
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  i2c_dly();
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  SDA = 0;
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  i2c_dly();
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  SCL = 0;
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  i2c_dly();
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}
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void i2c_stop(void)
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{
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  SDA = 0;            // i2c stop bit sequence
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  i2c_dly();
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  SCL = 1;
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  i2c_dly();
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  SDA = 1;
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  i2c_dly();
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}
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unsigned char i2c_rx(char ack)
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{
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char x, d=0;
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  SDA = 1;
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  for(x=0; x<8; x++) {
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    d <<= 1;
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    do {
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      SCL = 1;
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    }
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    while(SCL_IN==0);    // wait for any SCL clock stretching
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    i2c_dly();
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    if(SDA_IN) d |= 1;
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    SCL = 0;
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  }
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  if(ack) SDA = 0;
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  else SDA = 1;
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  SCL = 1;
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  i2c_dly();            // send (N)ACK bit
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  SCL = 0;
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  SDA = 1;
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  return d;
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}
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bit i2c_tx(unsigned char d)
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{
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char x;
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static bit b;
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  for(x=8; x; x--) {
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    if(d&0x80) SDA = 1;
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    else SDA = 0;
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    SCL = 1;
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    d <<= 1;
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    SCL = 0;
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  }
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  SDA = 1;
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  SCL = 1;
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  i2c_dly();
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  b = SDA_IN;          // possible ACK bit
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  SCL = 0;
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  return b;
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}
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The 4 primitive functions above can easily be put together to form complete I2C transactions. Here's and example to start an SRF08 ranging in cm:
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 +
i2c_start();              // send start sequence
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i2c_tx(0xE0);            // SRF08 I2C address with R/W bit clear
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i2c_tx(0x00);            // SRF08 command register address
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i2c_tx(0x51);            // command to start ranging in cm
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i2c_stop();              // send stop sequence
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Now after waiting 65mS for the ranging to complete (I've left that to you) the following example shows how to read the light sensor value from register 1 and the range result from registers 2 & 3.
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 +
i2c_start();              // send start sequence
 +
i2c_tx(0xE0);            // SRF08 I2C address with R/W bit clear
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i2c_tx(0x01);            // SRF08 light sensor register address
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i2c_start();              // send a restart sequence
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i2c_tx(0xE1);            // SRF08 I2C address with R/W bit set
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lightsensor = i2c_rx(1);  // get light sensor and send acknowledge. Internal register address will increment automatically.
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rangehigh = i2c_rx(1);    // get the high byte of the range and send acknowledge.
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rangelow = i2c_rx(0);    // get low byte of the range - note we don't acknowledge the last byte.
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i2c_stop();              // send stop sequence
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 +
</source>
  
 
<br><br>
 
<br><br>

2015年12月1日 (二) 09:26的版本

1 概述

两根线： SDA， SCL



2 软件实现 

#define SCL     TRISB4 // I2C bus
#define SDA     TRISB1 //
#define SCL_IN  RB4    //
#define SDA_IN  RB1    //

To initialize the ports set the output resisters to 0 and the tristate registers to 1 which disables the outputs and allows them to be pulled high by the resistors.
SDA = SCL = 1;
SCL_IN = SDA_IN = 0;

We use a small delay routine between SDA and SCL changes to give a clear sequence on the I2C bus. This is nothing more than a subroutine call and return.
void i2c_dly(void)
{
}

The following 4 functions provide the primitive start, stop, read and write sequences. All I2C transactions can be built up from these.
void i2c_start(void)
{
  SDA = 1;             // i2c start bit sequence
  i2c_dly();
  SCL = 1;
  i2c_dly();
  SDA = 0;
  i2c_dly();
  SCL = 0;
  i2c_dly();
}

void i2c_stop(void)
{
  SDA = 0;             // i2c stop bit sequence
  i2c_dly();
  SCL = 1;
  i2c_dly();
  SDA = 1;
  i2c_dly();
}

unsigned char i2c_rx(char ack)
{
char x, d=0;
  SDA = 1; 
  for(x=0; x<8; x++) {
    d <<= 1;
    do {
      SCL = 1;
    }
    while(SCL_IN==0);    // wait for any SCL clock stretching
    i2c_dly();
    if(SDA_IN) d |= 1;
    SCL = 0;
  } 
  if(ack) SDA = 0;
  else SDA = 1;
  SCL = 1;
  i2c_dly();             // send (N)ACK bit
  SCL = 0;
  SDA = 1;
  return d;
}

bit i2c_tx(unsigned char d)
{
char x;
static bit b;
  for(x=8; x; x--) {
    if(d&0x80) SDA = 1;
    else SDA = 0;
    SCL = 1;
    d <<= 1;
    SCL = 0;
  }
  SDA = 1;
  SCL = 1;
  i2c_dly();
  b = SDA_IN;          // possible ACK bit
  SCL = 0;
  return b;
}

The 4 primitive functions above can easily be put together to form complete I2C transactions. Here's and example to start an SRF08 ranging in cm:

i2c_start();              // send start sequence
i2c_tx(0xE0);             // SRF08 I2C address with R/W bit clear
i2c_tx(0x00);             // SRF08 command register address
i2c_tx(0x51);             // command to start ranging in cm
i2c_stop();               // send stop sequence

Now after waiting 65mS for the ranging to complete (I've left that to you) the following example shows how to read the light sensor value from register 1 and the range result from registers 2 & 3.

i2c_start();              // send start sequence
i2c_tx(0xE0);             // SRF08 I2C address with R/W bit clear
i2c_tx(0x01);             // SRF08 light sensor register address
i2c_start();              // send a restart sequence
i2c_tx(0xE1);             // SRF08 I2C address with R/W bit set
lightsensor = i2c_rx(1);  // get light sensor and send acknowledge. Internal register address will increment automatically.
rangehigh = i2c_rx(1);    // get the high byte of the range and send acknowledge.
rangelow = i2c_rx(0);     // get low byte of the range - note we don't acknowledge the last byte.
i2c_stop();               // send stop sequence



3 参考































来自“http://wiki.jackslab.org/index.php?title=I2C_%E6%80%BB%E7%BA%BF%E7%B2%BE%E8%A6%81&oldid=5131”
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