The mikroBasic 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
dim Soft_I2C_Scl           as sbit at RF3_bit
    Soft_I2C_Sda           as sbit at RF2_bit
    Soft_I2C_Scl_Direction as sbit at TRISF3_bit
    Soft_I2C_Sda_Direction as sbit at TRISF2_bit
' End Software I2C connections
...
Soft_I2C_Init()

Soft_I2C_Start

' Issue START signal
Soft_I2C_Start()

Soft_I2C_Read

dim take as byte
...
' Read data and send the not_acknowledge signal
take = Soft_I2C_Read(0)

Soft_I2C_Write

dim data_, error as byte
...
error = Soft_I2C_Write(data_)
error = Soft_I2C_Write($A3)

Soft_I2C_Stop

' Issue STOP signal
Soft_I2C_Stop()

Soft_I2C_Break

dim data1, error, counter as byte

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

main:

  ...

  ' 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

dim seconds, minutes, hours, day, month_, year as byte    ' Global date/time variables

' Software I2C connections
dim Soft_I2C_Scl           as sbit at RF3_bit
    Soft_I2C_Sda           as sbit at RF2_bit
    Soft_I2C_Scl_Direction as sbit at TRISF3_bit
    Soft_I2C_Sda_Direction as sbit at TRISF2_bit
' End Software I2C connections

' LCD module connections
dim LCD_RS as sbit at LATD0_bit
dim LCD_EN as sbit at LATD1_bit
dim LCD_D4 as sbit at LATB0_bit
dim LCD_D5 as sbit at LATB1_bit
dim LCD_D6 as sbit at LATB2_bit
dim LCD_D7 as sbit at LATB3_bit

dim LCD_RS_Direction as sbit at TRISD0_bit
dim LCD_EN_Direction as sbit at TRISD1_bit
dim LCD_D4_Direction as sbit at TRISB0_bit
dim LCD_D5_Direction as sbit at TRISB1_bit
dim LCD_D6_Direction as sbit at TRISB2_bit
dim LCD_D7_Direction as sbit at TRISB3_bit
' End LCD module connections

'--------------------- Reads time and date information from RTC (PCF8583)
sub procedure 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}
end sub

'-------------------- Formats date and time
sub procedure Transform_Time()
  seconds =  ((seconds and 0xF0) >> 4)*10 + (seconds and 0x0F)  ' Transform seconds
  minutes =  ((minutes and 0xF0) >> 4)*10 + (minutes and 0x0F)  ' Transform months
  hours   =  ((hours and 0xF0)  >> 4)*10  + (hours and 0x0F)    ' Transform hours
  year    =   (day and 0xC0) >> 6                               ' Transform year
  day     =  ((day and 0x30) >> 4)*10    + (day and 0x0F)       ' Transform day
  month_  =  ((month_ and 0x10)  >> 4)*10 + (month_ and 0x0F)   ' Transform month
end sub

'-------------------- Output values to LCD
sub procedure Display_Time()
  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 sub

'------------------ Performs project-wide init
sub procedure 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")
end sub

'----------------- Main procedure
main:

  Delay_ms(1000)

  Init_Main()              ' Perform initialization

  while TRUE               ' Endless loop
    Read_Time()            ' Read time from RTC(PCF8583)
    Transform_Time()       ' Format date and time
    Display_Time()         ' Prepare and display on LCD
  wend
end.

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