Software I²C Library

The mikroC 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

The following variables must be defined in all projects using Software I²C Library:	Description :	Example :
`extern sfr sbit bdata Soft_I2C_Scl;`	Soft I²C Clock line.	`sbit Soft_I2C_Scl at P1_0_bit;`
`extern sfr sbit bdata Soft_I2C_Sda;`	Soft I²C Data line.	`sbit Soft_I2C_Sda at P1_1_bit;`

Soft_I2C_Init

Prototype	void Soft_I2C_Init();
Returns	Nothing.
Description	Configures the software I²C module.
Requires	`Soft_I2C_Scl` and `Soft_I2C_Sda` variables must be defined before using this function.
Example	// soft_i2c pinout definition sbit Soft_I2C_Scl at P1_0_bit; sbit Soft_I2C_Sda at P1_1_bit; ... Soft_I2C_Init();

Soft_I2C_Start

Prototype	void Soft_I2C_Start(void);
Returns	Nothing.
Description	Determines if the I²C bus is free and issues START signal.
Requires	Software I²C must be configured before using this function. See Soft_I2C_Init routine.
Example	// Issue START signal Soft_I2C_Start();

Soft_I2C_Read

Prototype	unsigned short Soft_I2C_Read(unsigned int ack);
Returns	One byte from the Slave.
Description	Reads one byte from the slave. Parameters : `ack:` acknowledge signal parameter. If the `ack==0` not acknowledge signal will be sent after reading, otherwise the acknowledge signal will be sent.
Requires	Soft I²C must be configured before using this function. See Soft_I2C_Init routine. Also, START signal needs to be issued in order to use this function. See Soft_I2C_Start routine.
Example	unsigned short take; ... // Read data and send the not_acknowledge signal take = Soft_I2C_Read(0);

Soft_I2C_Write

Prototype	unsigned short Soft_I2C_Write(unsigned short data_);
Returns	`0` if there were no errors. `1` if write collision was detected on the I²C bus.
Description	Sends data byte via the I²C bus. Parameters : `_Data:` data to be sent
Requires	Soft I²C must be configured before using this function. See Soft_I2C_Init routine. Also, START signal needs to be issued in order to use this function. See Soft_I2C_Start routine.
Example	unsigned short data_, error; ... error = Soft_I2C_Write(data_); error = Soft_I2C_Write(0xA3);

Soft_I2C_Stop

Prototype	void Soft_I2C_Stop(void);
Returns	Nothing.
Description	Issues STOP signal.
Requires	Soft I²C must be configured before using this function. See Soft_I2C_Init routine.
Example	// 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	char counter = 0; void Timer1InterruptHandler() org IVT_ADDR_ET1{ if (counter >= 20) { Soft_I2C_Break(); counter = 0; // reset counter } else counter++; // increment counter } void main() { 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 ... }

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 from the RTC and prints it on Lcd.

char seconds, minutes, hours, date, month;  // Global date/time variables
unsigned int year;
unsigned int RTCModuleAddress, YearOffset; // RTC chip description variables

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

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

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

//------------------ Performs project-wide init
void Init_Main() {

  #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,':');
}

//--------------------- Reads time and date information from PCF8583 RTC
void Read_Time_PCF8583() {
  char byte_read;
  
  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 & 0xF0) >> 4)*10 + (byte_read & 0x0F); // Transform seconds

  byte_read = Soft_I2C_Read(1);                                // Read minutes byte
  minutes = ((byte_read & 0xF0) >> 4)*10 + (byte_read & 0x0F); // Transform minutes

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

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

  byte_read = Soft_I2C_Read(0);                                // Read weekday/month byte
  month = ((byte_read & 0x10) >> 4)*10 + (byte_read & 0x0F);   // Transform month

  Soft_I2C_Stop();                    // Issue stop signal
}

//--------------------- Reads time and date information from DS1307 RTC
void Read_Time_DS1307() {
  char byte_read;

  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 & 0x70) >> 4)*10 + (byte_read & 0x0F); // Transform seconds

  byte_read = Soft_I2C_Read(1);                                // Read minutes byte
  minutes = ((byte_read & 0x70) >> 4)*10 + (byte_read & 0x0F); // Transform minutes

  byte_read = Soft_I2C_Read(1);                                // Read hours byte
  if (byte_read.B6) {                                          // 12h format
    hours = ((byte_read & 0x10) >> 4)*10 + (byte_read & 0x0F); // Transform hours
    if (byte_read.B5)                                          // PM flag
      hours = hours + 12;
  }
  else
    hours = ((byte_read & 0x30) >> 4)*10 + (byte_read & 0x0F); // Transform hours

  byte_read = Soft_I2C_Read(1);                                // Read weekday byte
  
  byte_read = Soft_I2C_Read(1);                                // Read date byte
  date = ((byte_read & 0x30) >> 4)*10 + (byte_read & 0x0F);    // Transform date
  
  byte_read = Soft_I2C_Read(1);                                // Read month byte
  month = ((byte_read & 0x10) >> 4)*10 + (byte_read & 0x0F);   // Transform month
  
  byte_read = Soft_I2C_Read(1);                                // Read year byte
  year = YearOffset + ((byte_read & 0xF0) >> 4)*10 + (byte_read & 0x0F); // Transform year

  Soft_I2C_Stop();                    // Issue stop signal
}

//--------------------- Reads time and date information from RTC
void Read_Time() {
  #ifdef PCF8583
    Read_Time_PCF8583();
  #endif

  #ifdef DS1307
    Read_Time_DS1307();
  #endif
}

//-------------------- Output values to LCD
void Display_Time() {

  Lcd_Chr(1, 6, (date / 10)   + 48);    // Print tens digit of date variable
  Lcd_Chr(1, 7, (date % 10)   + 48);    // Print oness digit of date variable
  Lcd_Chr(1, 9, (month / 10)  + 48);
  Lcd_Chr(1,10, (month % 10)  + 48);
  Lcd_Chr(1,12, ((year / 1000) % 10) + 48);    // Print year
  Lcd_Chr(1,13, ((year / 100)  % 10) + 48);
  Lcd_Chr(1,14, ((year / 10)   % 10) + 48);
  Lcd_Chr(1,15, (year % 10)          + 48);

  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);
}

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

  Delay_ms(2000);

  Init_Main();               // Perform initialization

  while (1) {                // Endless loop
    Read_Time();             // Read time from RTC
    Display_Time();          // Prepare and display on LCD

    Delay_ms(1000);          // Wait 1 second
  }
}

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