The mikroPascal PRO for 8051 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.

Notes:

• 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.

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 P1_0_bit;
    Soft_I2C_Sda : sbit at P1_1_bit;
...
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

var counter : byte;

procedure Timer1InterruptHandler(); org IVT_ADDR_ET1;
begin
  counter := 0;
  if (counter >= 20)
    begin
      Soft_I2C_Break();
      counter := 0;              // reset counter
    end
  else
    Inc(counter);                // increment counter
end;

begin 

  TR1_bit := 0;                  // Stop Timer1  
  ET1_bit := 1;                  // Enable Timer1 interrupt
  TH1 := 0x00;                   // Set Timer1 high byte
  TL1 := 0x00;                   // Set Timer1 low byte
  TR1_bit := 1;                  // Run Timer1

  EA_bit := 0;                   // Interrupt disable

  ...

  // try Soft_I2C_Init with blocking prevention mechanism
  EA_bit := 1;                   // Interrupt enable
  Soft_I2C_Init();
  EA_bit := 0;                   // Interrupt disable

  ...

end.

Library Example

The example demonstrates Software I²C Library routines usage. The 8051 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.

program RTC_Read;

var seconds, minutes, hours, date, month : byte;    // Global date/time variables
var year, RTCModuleAddress, YearOffset : word;

{$DEFINE PCF8583}// Uncomment this line if you use PCF8583 RTC chip (mE RTC extra board)
//{$DEFINE DS1307}// Uncomment this line if you use DS1307 RTC chip (mE RTC2 extra board)

// Software I2C connections
var Soft_I2C_Scl : sbit at P1_0_bit;
var Soft_I2C_Sda : sbit at P1_1_bit;
// End Software I2C connections

// LCD module connections
var LCD_RS : sbit at P2_0_bit;
var LCD_EN : sbit at P2_1_bit;

var LCD_D4 : sbit at P2_2_bit;
var LCD_D5 : sbit at P2_3_bit;
var LCD_D6 : sbit at P2_4_bit;
var LCD_D7 : sbit at P2_5_bit;
// End LCD module connections

//------------------ Performs project-wide init
procedure Init_Main();
  begin
    {$IFDEF PCF8583}
      RTCModuleAddress   := 0xA0;
      YearOffset         := 2008;
    {$ENDIF}

    {$IFDEF DS1307}
      RTCModuleAddress   := 0xD0;
      YearOffset         := 2000;
    {$ENDIF}


    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,':');
  end;

//--------------------- Reads time and date information from PCF8583 RTC
procedure Read_Time_PCF8583();
var byte_read : byte;
  begin
    Soft_I2C_Start();                   // Issue start signal
    Soft_I2C_Write(RTCModuleAddress);   // RTC module address + write (R#/W = 0)
    Soft_I2C_Write(2);                  // Start from seconds byte
    Soft_I2C_Start();                   // Issue repeated start signal
    Soft_I2C_Write(RTCModuleAddress+1); // RTC module address + read  (R#/W = 1)

    byte_read := Soft_I2C_Read(1);                                      // Read seconds byte
    seconds := ((byte_read and 0xF0) shr 4)*10 + (byte_read and 0x0F);  // Transform seconds

    byte_read := Soft_I2C_Read(1);                                      // Read minutes byte
    minutes := ((byte_read and 0xF0) shr 4)*10 + (byte_read and 0x0F);  // Transform minutes

    byte_read := Soft_I2C_Read(1);                                      // Read hours byte
    hours := ((byte_read and 0xF0) shr 4)*10 + (byte_read and 0x0F);    // Transform hours
    if ( (byte_read.B7) and (byte_read.B6) ) then                       // 12h format && PM flag
      hours := hours + 12;

    byte_read := Soft_I2C_Read(1);                                      // Read year/date byte
    year := YearOffset + ((byte_read and 0xC0) shr 6);                  // Transform year
    date := ((byte_read and 0x30) shr 4)*10 + (byte_read and 0x0F);     // Transform date

    byte_read := Soft_I2C_Read(0);                                      // Read weekday/month byte
    month := ((byte_read and 0x10) shr 4)*10 + (byte_read and 0x0F);    // Transform month

    Soft_I2C_Stop();                    // Issue stop signal
  end;

//--------------------- Reads time and date information from DS1307 RTC
procedure Read_Time_DS1307();
var byte_read : byte;
  begin
    Soft_I2C_Start();                   // Issue start signal
    Soft_I2C_Write(RTCModuleAddress);   // RTC module address + write (R#/W = 0)
    Soft_I2C_Write(0);                  // Start from seconds byte
    Soft_I2C_Start();                   // Issue repeated start signal
    Soft_I2C_Write(RTCModuleAddress+1); // RTC module address + read  (R#/W = 1)

    byte_read := Soft_I2C_Read(1);                                // Read seconds byte
    seconds := ((byte_read and 0x70) shr 4)*10 + (byte_read and 0x0F); // Transform seconds

    byte_read := Soft_I2C_Read(1);                                // Read minutes byte
    minutes := ((byte_read and 0x70) shr 4)*10 + (byte_read and 0x0F); // Transform minutes

    byte_read := Soft_I2C_Read(1);                                // Read hours byte
    if (byte_read.B6) then                                          // 12h format
      begin
        hours := ((byte_read and 0x10) shr 4)*10 + (byte_read and 0x0F); // Transform hours
        if (byte_read.B5) then                                         // PM flag
          hours := hours + 12;
      end
    else
      hours := ((byte_read and 0x30) shr 4)*10 + (byte_read and 0x0F); // Transform hours

    byte_read := Soft_I2C_Read(1);                                // Read weekday byte

    byte_read := Soft_I2C_Read(1);                                // Read date byte
    date := ((byte_read and 0x30) shr 4)*10 + (byte_read and 0x0F);    // Transform date

    byte_read := Soft_I2C_Read(1);                                // Read month byte
    month := ((byte_read and 0x10) shr 4)*10 + (byte_read and 0x0F);   // Transform month

    byte_read := Soft_I2C_Read(1);                                // Read year byte
    year := YearOffset + ((byte_read and 0xF0) shr 4)*10 + (byte_read and 0x0F); // Transform year

    Soft_I2C_Stop();                    // Issue stop signal
  end;
  
//--------------------- Reads time and date information from RTC
procedure Read_Time();
  begin
    {$IFDEF PCF8583}
      Read_Time_PCF8583();
    {$ENDIF}

    {$IFDEF DS1307}
      Read_Time_DS1307();
    {$ENDIF}
  end;


//-------------------- Output values to LCD
procedure Display_Time();
  begin
    Lcd_Chr(1, 6, (date div 10)   + 48);    // Print tens digit of date variable
    Lcd_Chr(1, 7, (date mod 10)   + 48);    // Print oness digit of date variable
    Lcd_Chr(1, 9, (month div 10)  + 48);
    Lcd_Chr(1,10, (month mod 10)  + 48);
    Lcd_Chr(1,12, (word(year div 1000) mod 10) + 48);    // Print year
    Lcd_Chr(1,13, (word(year div 100)  mod 10) + 48);
    Lcd_Chr(1,14, (word(year div 10)   mod 10) + 48);
    Lcd_Chr(1,15,  word(year mod 10)          + 48);

    Lcd_Chr(2, 6, (hours div 10)   + 48);
    Lcd_Chr(2, 7, (hours mod 10)   + 48);
    Lcd_Chr(2, 9, (minutes div 10) + 48);
    Lcd_Chr(2,10, (minutes mod 10) + 48);
    Lcd_Chr(2,12, (seconds div 10) + 48);
    Lcd_Chr(2,13, (seconds mod 10) + 48);
  end;

//----------------- Main procedure
  begin
    Delay_ms(2000);
    Init_Main();               // Perform initialization

    while TRUE do              // Endless loop
      begin
        Read_Time();             // Read time from RTC
        Display_Time();          // Prepare and display on LCD

        Delay_ms(1000);          // Wait 1 second
      end;
  end.

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