The mikroC PRO for AVR provides routines for implementing Software I²C communication. These routines are hardware independent and can be used with any MCU. The Software I²C library enables you to use MCU as Master in I²C communication. Multi-master mode is not supported.

  Important :

• This library implements time-based activities, so interrupts need to be disabled when using Software I²C.
• All I²C Library functions are blocking-call functions (they are waiting for I²C clock line to become logical one).
• The pins used for the Software I²C communication should be connected to the pull-up resistors. Turning off the LEDs connected to these pins may also be required.
• Every Software I²C library routine has its own counterpart in Hardware I²C library, except I2C_Repeated_Start. Soft_I2C_Start is used instead of I2C_Repeated_Start.
• Working clock frequency of the Software I²C is 20kHz.

External dependencies of Software I²C Library

Library Routines

• Soft_I2C_Init
• Soft_I2C_Start
• Soft_I2C_Read
• Soft_I2C_Write
• Soft_I2C_Stop
• Soft_I2C_Break

Soft_I2C_Init

// Software I2C connections
sbit Soft_I2C_Scl_Output    at PORTC0_bit;
sbit Soft_I2C_Sda_Output    at PORTC1_bit;
sbit Soft_I2C_Scl_Input     at PINC0_bit;
sbit Soft_I2C_Sda_Input     at PINC1_bit;
sbit Soft_I2C_Scl_Direction at DDC0_bit;
sbit Soft_I2C_Sda_Direction at DDC1_bit;
// End Software I2C connections

...
Soft_I2C_Init();

Soft_I2C_Start

// Issue START signal
Soft_I2C_Start();

Soft_I2C_Read

unsigned short take;
...
// Read data and send the not_acknowledge signal
take = Soft_I2C_Read(0);

Soft_I2C_Write

unsigned short data_, error;
...
error = Soft_I2C_Write(data_);
error = Soft_I2C_Write(0xA3);

Soft_I2C_Stop

// Issue STOP signal
Soft_I2C_Stop();

Soft_I2C_Break

Prototype	void Soft_I2C_Break(void);
Returns	Nothing.
Description	All Software I²C Library functions can block the program flow (see note at the top of this page). Calling this routine from interrupt will unblock the program execution. This mechanism is similar to WDT.   Note : Interrupts should be disabled before using Software I²C routines again (see note at the top of this page).
Requires	Nothing.
Example	// Software I2C connections sbit Soft_I2C_Scl_Output at PORTC0_bit; sbit Soft_I2C_Sda_Output at PORTC1_bit; sbit Soft_I2C_Scl_Input at PINC0_bit; sbit Soft_I2C_Sda_Input at PINC1_bit; sbit Soft_I2C_Scl_Direction at DDC0_bit; sbit Soft_I2C_Sda_Direction at DDC1_bit; // End Software I2C connections char counter = 0; void Timer0Overflow_ISR() org 0x12 { if (counter >= 20) { Soft_I2C_Break(); counter = 0; // reset counter } else counter++; // increment counter } void main() { TOIE0_bit = 1; // Timer0 overflow interrupt enable TCCR0_bit = 5; // Start timer with 1024 prescaler SREG_I_bit = 0; // Interrupt disable ... // try Soft_I2C_Init with blocking prevention mechanism SREG_I_bit = 1; // Interrupt enable Soft_I2C_Init(); SREG_I_bit = 0; // Interrupt disable ... }

Library Example

The example demonstrates Software I²C Library routines usage. The AVR MCU is connected (SCL, SDA pins) to PCF8583 RTC (real-time clock). Program reads date and time are read from the RTC and prints it on Lcd.

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char seconds, minutes, hours, day, month, year;    // Global date/time variables

// Software I2C connections
sbit Soft_I2C_Scl_Output    at PORTC0_bit;
sbit Soft_I2C_Sda_Output    at PORTC1_bit;
sbit Soft_I2C_Scl_Input     at PINC0_bit;
sbit Soft_I2C_Sda_Input     at PINC1_bit;
sbit Soft_I2C_Scl_Direction at DDC0_bit;
sbit Soft_I2C_Sda_Direction at DDC1_bit;
// End Software I2C connections

// LCD module connections
sbit LCD_RS at PORTD2_bit;
sbit LCD_EN at PORTD3_bit;
sbit LCD_D4 at PORTD4_bit;
sbit LCD_D5 at PORTD5_bit;
sbit LCD_D6 at PORTD6_bit;
sbit LCD_D7 at PORTD7_bit;

sbit LCD_RS_Direction at DDD2_bit;
sbit LCD_EN_Direction at DDD3_bit;
sbit LCD_D4_Direction at DDD4_bit;
sbit LCD_D5_Direction at DDD5_bit;
sbit LCD_D6_Direction at DDD6_bit;
sbit LCD_D7_Direction at DDD7_bit;
// End LCD module connections

//--------------------- Reads time and date information from RTC (PCF8583)
void Read_Time() {

  Soft_I2C_Start();               // Issue start signal
  Soft_I2C_Write(0xA0);           // Address PCF8583, see PCF8583 datasheet
  Soft_I2C_Write(2);              // Start from address 2
  Soft_I2C_Start();               // Issue repeated start signal
  Soft_I2C_Write(0xA1);           // Address PCF8583 for reading R/W=1
  
  seconds = Soft_I2C_Read(1);     // Read seconds byte
  minutes = Soft_I2C_Read(1);     // Read minutes byte
  hours = Soft_I2C_Read(1);       // Read hours byte
  day = Soft_I2C_Read(1);         // Read year/day byte
  month = Soft_I2C_Read(0);       // Read weekday/month byte
  Soft_I2C_Stop();                // Issue stop signal
  
}

//-------------------- Formats date and time
void Transform_Time() {
  seconds  =  ((seconds & 0xF0) >> 4)*10 + (seconds & 0x0F);  // Transform seconds
  minutes  =  ((minutes & 0xF0) >> 4)*10 + (minutes & 0x0F);  // Transform months
  hours    =  ((hours & 0xF0)  >> 4)*10  + (hours & 0x0F);    // Transform hours
  year     =   (day & 0xC0) >> 6;                             // Transform year
  day      =  ((day & 0x30) >> 4)*10    + (day & 0x0F);       // Transform day
  month    =  ((month & 0x10)  >> 4)*10 + (month & 0x0F);     // Transform month
}

//-------------------- Output values to LCD
void Display_Time() {

   Lcd_Chr(1, 6, (day / 10)   + 48);    // Print tens digit of day variable
   Lcd_Chr(1, 7, (day % 10)   + 48);    // Print oness digit of day variable
   Lcd_Chr(1, 9, (month / 10) + 48);
   Lcd_Chr(1,10, (month % 10) + 48);
   Lcd_Chr(1,15,  year        + 56);    // Print year vaiable + 8 (start from year 2008)

   Lcd_Chr(2, 6, (hours / 10)   + 48);
   Lcd_Chr(2, 7, (hours % 10)   + 48);
   Lcd_Chr(2, 9, (minutes / 10) + 48);
   Lcd_Chr(2,10, (minutes % 10) + 48);
   Lcd_Chr(2,12, (seconds / 10) + 48);
   Lcd_Chr(2,13, (seconds % 10) + 48);
}

//------------------ Performs project-wide init
void Init_Main() {
  
  Soft_I2C_Init();           // Initialize Soft I2C communication
  
  Lcd_Init();                // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);        // Clear LCD display
  Lcd_Cmd(_LCD_CURSOR_OFF);   // Turn cursor off

  Lcd_Out(1,1,"Date:");      // Prepare and output static text on LCD
  Lcd_Chr(1,8,':');
  Lcd_Chr(1,11,':');
  Lcd_Out(2,1,"Time:");
  Lcd_Chr(2,8,':');
  Lcd_Chr(2,11,':');
  Lcd_Out(1,12,"200");
}

//----------------- Main procedure
void main() {
  Init_Main();               // Perform initialization

  while (1) {                // Endless loop
    Read_Time();             // Read time from RTC(PCF8583)
    Transform_Time();        // Format date and time
    Display_Time();          // Prepare and display on LCD

    Delay_ms(1000);          // Wait 1 second
  }
}

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