The mikroC 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
sbit Soft_I2C_Scl           at RB11_bit;
sbit Soft_I2C_Sda           at RB12_bit;
sbit Soft_I2C_Scl_Direction at TRISB11_bit;
sbit Soft_I2C_Sda_Direction at TRISB12_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

// Software I2C connections
sbit Soft_I2C_Scl           at RC0_bit;
sbit Soft_I2C_Sda           at RC1_bit;
sbit Soft_I2C_Scl_Direction at TRISC0_bit;
sbit Soft_I2C_Sda_Direction at TRISC1_bit;
// End Software I2C connections

char counter = 0;

void Timer1Int() org IVT_ADDR_T1INTERRUPT {

  if (counter >= 20) {
    Soft_I2C_Break();
    counter = 0;                // reset counter
  }
  
  else
    counter++;                  // increment counter
  
  T1IF_bit = 0;                 // Clear Timer1 overflow interrupt flag
}

void main() {

  ...
  
  // try Soft_I2C_Init with blocking prevention mechanism
  IPC0   = IPC0 | 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
}

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

// Software I2C connections
sbit Soft_I2C_Scl           at RB11_bit;
sbit Soft_I2C_Sda           at RB12_bit;
sbit Soft_I2C_Scl_Direction at TRISB11_bit;
sbit Soft_I2C_Sda_Direction at TRISB12_bit;
// End Software I2C connections

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

sbit LCD_RS_Direction at TRISD0_bit;
sbit LCD_EN_Direction at TRISD1_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_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() {
  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");
}

//----------------- Main procedure
void main() {

  Delay_ms(2000);

  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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