The mikroPascal PRO for dsPIC30/33 and PIC24 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 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
var Soft_I2C_Scl           : sbit at RF3_bit;
    Soft_I2C_Sda           : sbit at RF2_bit;
    Soft_I2C_Scl_Direction : sbit at TRISF3_bit;
    Soft_I2C_Sda_Direction : sbit at TRISF2_bit;
// End Software I2C connections
...
Soft_I2C_Init();

Soft_I2C_Start

// Issue START signal
Soft_I2C_Start();

Soft_I2C_Read

var take : byte;
...
// 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($A3);

Soft_I2C_Stop

// Issue STOP signal
Soft_I2C_Stop();

Soft_I2C_Break

var data1, error, counter : byte;

procedure Timer1Int(); org IVT_ADDR_T1INTERRUPT;
begin
  counter := 0;
  if (counter >= 20)
    begin
      Soft_I2C_Break();
      counter := 0;                // reset counter
    end
  else
    Inc(counter);                  // increment counter
 
  T1IF_bit := 0;                 // Clear Timer1 overflow interrupt flag
end;

begin 

  ...

  // try Soft_I2C_Init with blocking prevention mechanism
  IPC0   := IPC0 or 0x1000;       // Interrupt priority level = 1 
  T1IE_bit := 1;                 // Enable Timer1 interrupts
  T1CON := 0x8030;               // Timer1 ON, internal clock FCY, prescaler 1:256
  Soft_I2C_Init();
  T1IE_bit := 0;                 // Disable Timer1 interrupts

end.

Library Example

The example demonstrates use of the Software I²C Library. The dsPIC30/33 or PIC24 MCU is connected (SCL, SDA pins) to PCF8583 RTC (real-time clock). Program sends date/time to RTC.

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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 RF3_bit;
    Soft_I2C_Sda           : sbit at RF2_bit;
    Soft_I2C_Scl_Direction : sbit at TRISF3_bit;
    Soft_I2C_Sda_Direction : sbit at TRISF2_bit;
// End Software I2C connections

// LCD module connections
var LCD_RS : sbit at LATD0_bit;
var LCD_EN : sbit at LATD1_bit;
var LCD_D4 : sbit at LATB0_bit;
var LCD_D5 : sbit at LATB1_bit;
var LCD_D6 : sbit at LATB2_bit;
var LCD_D7 : sbit at LATB3_bit;

var LCD_RS_Direction : sbit at TRISD0_bit;
var LCD_EN_Direction : sbit at TRISD1_bit;
var LCD_D4_Direction : sbit at TRISB0_bit;
var LCD_D5_Direction : sbit at TRISB1_bit;
var LCD_D6_Direction : sbit at TRISB2_bit;
var 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        + 57);    // Print year vaiable + 9 (start from year 2009)

     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
    ADPCFG := 0xFFFF;           // initialize AN pins as digital

    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

   Delay_ms(1000);

   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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