The mikroPascal 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 Software 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.
• 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

// Soft_I2C pinout definition
var Soft_I2C_Scl_Output        : sbit at PORTC0_bit;     
var Soft_I2C_Sda_Output        : sbit at PORTC1_bit;      
var Soft_I2C_Scl_Input         : sbit at PINC0_bit;        
var Soft_I2C_Sda_Input         : sbit at PINC1_bit;        
var Soft_I2C_Scl_Direction : sbit at DDC0_bit;
var Soft_I2C_Sda_Direction : sbit at DDC1_bit;
// End of Soft_I2C pinout definition
...
Soft_I2C_Init();

Soft_I2C_Start

// Issue START signal
Soft_I2C_Start();

Soft_I2C_Read

var take : word;
...
// Read data and send the not_acknowledge signal
take := Soft_I2C_Read(0);

Soft_I2C_Write

var data_, error : byte;
...
error := Soft_I2C_Write(data_);
error := Soft_I2C_Write(0xA3);

Soft_I2C_Stop

// Issue STOP signal
Soft_I2C_Stop();

Soft_I2C_Break

Prototype	procedure Soft_I2C_Break();
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	// Soft_I2C pinout definition var Soft_I2C_Scl_Output : sbit at PORTC0_bit; var Soft_I2C_Sda_Output : sbit at PORTC1_bit; var Soft_I2C_Scl_Input : sbit at PINC0_bit; var Soft_I2C_Sda_Input : sbit at PINC1_bit; var Soft_I2C_Scl_Direction : sbit at DDC0_bit; var Soft_I2C_Sda_Direction : sbit at DDC1_bit; // End of Soft_I2C pinout definition var counter : byte; procedure Timer0Overflow_ISR(); org 0x12; begin counter := 0; if (counter >= 20) begin Soft_I2C_Break(); counter := 0; // reset counter end else Inc(counter); // increment counter end; begin 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 ... end.

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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program RTC_Read;

var seconds, minutes, hours, day, month, year : byte;    // Global date/time variables

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

// LCD module connections
var LCD_RS : sbit at PORTD2_bit;
    LCD_EN : sbit at PORTD3_bit;
    LCD_D4 : sbit at PORTD4_bit;
    LCD_D5 : sbit at PORTD5_bit;
    LCD_D6 : sbit at PORTD6_bit;
    LCD_D7 : sbit at PORTD7_bit;
    LCD_RS_Direction : sbit at DDD2_bit;
    LCD_EN_Direction : sbit at DDD3_bit;
    LCD_D4_Direction : sbit at DDD4_bit;
    LCD_D5_Direction : sbit at DDD5_bit;
    LCD_D6_Direction : sbit at DDD6_bit;
    LCD_D7_Direction : sbit at DDD7_bit;
// End LCD module connections

//--------------------- Reads time and date information from RTC (PCF8583)
procedure Read_Time();
  begin
    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
  end;

//-------------------- Formats date and time
procedure Transform_Time() ;
  begin
    seconds  :=  ((seconds and 0xF0) shr 4)*10 + (seconds and 0x0F);  // Transform seconds
    minutes  :=  ((minutes and 0xF0) shr 4)*10 + (minutes and 0x0F);  // Transform months
    hours    :=  ((hours and 0xF0)  shr 4)*10  + (hours and 0x0F);    // Transform hours
    year     :=   (day and 0xC0) shr 6;                               // Transform year
    day      :=  ((day and 0x30) shr 4)*10    + (day and 0x0F);       // Transform day
    month    :=  ((month and 0x10)  shr 4)*10 + (month and 0x0F);     // Transform month
  end;

//-------------------- Output values to LCD
procedure Display_Time();
  begin
     Lcd_Chr(1, 6, (day / 10)   + 48);    // Print tens digit of day variable
     Lcd_Chr(1, 7, (day mod 10)   + 48);  // Print oness digit of day variable
     Lcd_Chr(1, 9, (month / 10) + 48);
     Lcd_Chr(1,10, (month mod 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 mod 10)   + 48);
     Lcd_Chr(2, 9, (minutes / 10) + 48);
     Lcd_Chr(2,10, (minutes mod 10) + 48);
     Lcd_Chr(2,12, (seconds / 10) + 48);
     Lcd_Chr(2,13, (seconds mod 10) + 48);
  end;

//------------------ Performs project-wide init
procedure Init_Main();
  begin
    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');
  end;

//----------------- Main procedure
  begin
   Init_Main();                // Perform initialization

    while TRUE do              // Endless loop
      begin
        Read_Time();           // Read time from RTC(PCF8583)
        Transform_Time();      // Format date and time
        Display_Time();        // Prepare and display on LCD
      end;
  end.

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