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/i2csw.c

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/*! \file i2csw.c \brief Software-driven I2C interface using port pins. */
//*****************************************************************************
//
// File Name    : 'i2csw.c'
// Title        : Software-driven I2C interface using port pins
// Author       : Pascal Stang
// Created      : 11/22/2000
// Revised      : 5/2/2002
// Version      : 1.1
// Target MCU   : Atmel AVR series
// Editor Tabs  : 4
//
// This code is distributed under the GNU Public License
//      which can be found at http://www.gnu.org/licenses/gpl.txt
//
//*****************************************************************************

#include <avr/io.h>

#include "i2csw.h"

// Standard I2C bit rates are:
// 100KHz for slow speed
// 400KHz for high speed

//#define QDEL  delay(5)        // i2c quarter-bit delay
//#define HDEL  delay(10)       // i2c half-bit delay

// i2c quarter-bit delay
#define QDEL    asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop");
// i2c half-bit delay
#define HDEL    asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop"); asm volatile("nop");

#define I2C_SDL_LO      cbi( SDAPORT, SDA)
#define I2C_SDL_HI      sbi( SDAPORT, SDA)

#define I2C_SCL_LO      cbi( SCLPORT, SCL); 
#define I2C_SCL_HI      sbi( SCLPORT, SCL); 

#define I2C_SCL_TOGGLE  HDEL; I2C_SCL_HI; HDEL; I2C_SCL_LO;
#define I2C_START       I2C_SDL_LO; QDEL; I2C_SCL_LO; 
#define I2C_STOP        HDEL; I2C_SCL_HI; QDEL; I2C_SDL_HI; HDEL;

/*
void i2ct(void)
{
    HDEL; I2C_SCL_HI; HDEL; I2C_SCL_LO;
}

void i2cstart(void)
{
    I2C_SDL_LO; QDEL; I2C_SCL_LO; 
}

void i2cstop(void)
{
    HDEL; I2C_SCL_HI; QDEL; I2C_SDL_HI; HDEL;
}


#define I2C_SCL_TOGGLE  i2ct();
#define I2C_START       i2cstart();
#define I2C_STOP        i2cstop();  
*/

UINT i2cPutbyte(u08 b)
{
    int i;
    
    for (i=7;i>=0;i--)
    {
        if ( b & (1<<i) )
            I2C_SDL_HI;
        else
            I2C_SDL_LO;         // address bit
            I2C_SCL_TOGGLE;     // clock HI, delay, then LO
    }

    I2C_SDL_HI;                 // leave SDL HI
    // added    
    cbi(SDADDR, SDA);           // change direction to input on SDA line (may not be needed)
    HDEL;
    I2C_SCL_HI;                 // clock back up
    b = inp(SDAPIN) & (1<<SDA); // get the ACK bit

    HDEL;
    I2C_SCL_LO;                 // not really ??
    sbi(SDADDR, SDA);           // change direction back to output
    HDEL;
    return (b == 0);            // return ACK value
}


u08 i2cGetbyte(UINT last)
{
    int i;
    u08 c,b = 0;
        
    I2C_SDL_HI;                 // make sure pullups are ativated
    cbi(SDADDR, SDA);           // change direction to input on SDA line (may not be needed)

    for(i=7;i>=0;i--)
    {
        HDEL;
        I2C_SCL_HI;             // clock HI
        c = inp(SDAPIN) & (1<<SDA);  
        b <<= 1;
        if(c) b |= 1;
        HDEL;
        I2C_SCL_LO;             // clock LO
    }

    sbi(SDADDR, SDA);           // change direction to output on SDA line
  
    if (last)
        I2C_SDL_HI;             // set NAK
    else
        I2C_SDL_LO;             // set ACK

    I2C_SCL_TOGGLE;             // clock pulse
    I2C_SDL_HI;                 // leave with SDL HI
    return b;                   // return received byte
}


//************************
//* I2C public functions *
//************************

//! Initialize I2C communication
void i2cInit(void)
{
    sbi( SDADDR, SDA);          // set SDA as output
    sbi( SCLDDR, SCL);          // set SCL as output
    I2C_SDL_HI;                 // set I/O state and pull-ups
    I2C_SCL_HI;                 // set I/O state and pull-ups
}

//! Send a byte sequence on the I2C bus
void i2cSend(u08 device, u08 subAddr, u08 length, u08 *data)
{
    I2C_START;                  // do start transition
    i2cPutbyte(device);         // send DEVICE address
    i2cPutbyte(subAddr);        // and the subaddress

    // send the data
    while (length--)
        i2cPutbyte(*data++);

    I2C_SDL_LO;                 // clear data line and
    I2C_STOP;                   // send STOP transition
}

//! Retrieve a byte sequence on the I2C bus
void i2cReceive(u08 device, u08 subAddr, u08 length, u08 *data)
{
    int j = length;
    u08 *p = data;

    I2C_START;                  // do start transition
    i2cPutbyte(device);         // send DEVICE address
    i2cPutbyte(subAddr);        // and the subaddress
    HDEL;
    I2C_SCL_HI;                 // do a repeated START
    I2C_START;                  // transition

    i2cPutbyte(device | READ);  // resend DEVICE, with READ bit set

    // receive data bytes
    while (j--)
        *p++ = i2cGetbyte(j == 0);

    I2C_SDL_LO;                 // clear data line and
    I2C_STOP;                   // send STOP transition
}

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