The mikroC 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 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 RC3_bit;
sbit Soft_I2C_Sda           at RC4_bit;
sbit Soft_I2C_Scl_Direction at TRISC3_bit;
sbit Soft_I2C_Sda_Direction at TRISC4_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 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 interrupt { if (INTCON.T0IF) { if (counter >= 20) { Soft_I2C_Break(); counter = 0; // reset counter } else counter++; // increment counter INTCON.T0IF = 0; // Clear Timer0 overflow interrupt flag } } void main() { 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 ... }

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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// Software I2C connections
sbit Soft_I2C_Scl           at RC3_bit;
sbit Soft_I2C_Sda           at RC4_bit;
sbit Soft_I2C_Scl_Direction at TRISC3_bit;
sbit Soft_I2C_Sda_Direction at TRISC4_bit;
// End Software I2C connections

// LCD module connections
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;

sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_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

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

//--------------------- 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        + 48);    // Print year variable  (start from year 2010)


   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() {

  TRISB = 0;
  PORTB = 0xFF;
  TRISB = 0xff;
  ANSEL  = 0;                // Configure AN pins as digital I/O
  ANSELH = 0;
  C1ON_bit = 0;              // Disable comparators
  C2ON_bit = 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
}

//----------------- Main procedure
void main() {
  Delay_ms(500);
   
  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
  }
}

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