The mikroPascal PRO for PIC 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.
• 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 Softvare 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               : sbit at RC3_bit;     
var Soft_I2C_Sda               : sbit at RC4_bit;      
var Soft_I2C_Scl_Direction : sbit at TRISC3_bit;
var Soft_I2C_Sda_Direction : sbit at TRISC4_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	var data1, error, counter : byte; procedure interrupt(); begin if (INTCON.T0IF <> 0) then if (counter >= 20) then begin Soft_I2C_Break(); counter := 0; // reset counter end else Inc(counter); // increment counter INTCON.T0IF := 0; // Clear Timer0 overflow interrupt flag end; begin counter := 0; OPTION_REG := 0x04; // TMR0 prescaler set to 1:32 ... // try Soft_I2C_Init with blocking prevention mechanism INTCON.GIE := 1; // Global interrupt enable INTCON.T0IE := 1; // Enable Timer0 overflow interrupt Soft_I2C_Init(); INTCON.GIE := 0; // Global interrupt disable end.

Library Example

The example demonstrates Software I²C Library routines usage. The PIC 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     : sbit at RC3_bit;
    Soft_I2C_Sda     : sbit at RC4_bit;
    Soft_I2C_Scl_Direction : sbit at TRISC3_bit;
    Soft_I2C_Sda_Direction : sbit at TRISC4_bit;
// End Software I2C connections

// LCD module connections
var LCD_RS : sbit at RB4_bit;
    LCD_EN : sbit at RB5_bit;
    LCD_D4 : sbit at RB0_bit;
    LCD_D5 : sbit at RB1_bit;
    LCD_D6 : sbit at RB2_bit;
    LCD_D7 : sbit at RB3_bit;
    LCD_RS_Direction : sbit at TRISB4_bit;
    LCD_EN_Direction : sbit at TRISB5_bit;
    LCD_D4_Direction : sbit at TRISB0_bit;
    LCD_D5_Direction : sbit at TRISB1_bit;
    LCD_D6_Direction : sbit at TRISB2_bit;
    LCD_D7_Direction : sbit at TRISB3_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        + 48);    // Print year variable

     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
  
    TRISB := 0;
    PORTB := 0xFF;
    TRISB := 0xff;
    ANSEL  := 0;                // Configure AN pins as digital I/O
    ANSELH := 0;
  
    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_Chr(1,16,'.');
    Lcd_Out(2,1,'Time:');
    Lcd_Chr(2,8,':');
    Lcd_Chr(2,11,':');
    Lcd_Out(1,12,'201');       // start from year 2010
  end;

//----------------- Main procedure
  begin
   Delay_ms(500);
   
   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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