Spency's digital-diy 18F PIC micro Tutorial

18F DS1307 Example

The DS1307 is a great piece of kit, it provides real time date and clock values, and interfaces with the PIC micro via I2C. The values it holds for date/time are, Secs, Mins, Hours, Day, Date, Month and Year. I hear you asking, why use this when you could make a small program do the same with a PIC;

The DS1307 has leap year compensation until 2100

A 32.768Khz crystal is far more accurate than a 4Mhz+ crystal

In back-up mode, the DS1307 consumes less than 500nA

Example of interfacing with a DS1307. Note that on the DS1037 Pin 8 is connected to 5V, Pin 4 is connected to GND and Pin 3 is connected to ground if no backup battery is used!

(LCD, 5v Regulator and Contrast Control not shown for ease of illustration)

Note the PIC's power supply/oscillator are not shown

If you wish to use a battery backup for the DS1307, then connect the positive of the battery to Pin 3, and the earth to Pin 4. When ever Vcc (Pin 8) is lower than Pin 3 (Batt), the device will enter backup mode and consume less than 500nA.

Datasheet for the DS1307

Notice that the DS1307 also requires an external oscillator, both the chip and crystal (part# CRY32) can be found at Futurlec. Be sure to connect the 4.7K pull-up resistors on SCL and SDA as shown aswell.

Device = 18F452
Clock = 20

// some LCD options...
#option LCD_DATA = PORTD.4
#option LCD_RS = PORTD.2
#option LCD_EN = PORTD.3

// import LCD library...
Include "LCD.bas" 
Include "utils.bas"
Include "convert.bas"
Include "I2C.bas"

Structure TTime
   Second As Byte         // Second (0..59)
   Minute As Byte         // Minute (0..59)
   Hour As Byte           // Hour   (0..11 or 0..23)
End Structure

Structure TDate
   Day   As Byte          // Date  (0..31)
   Month As Byte          // Month (1..12)
   Year  As Byte          // Year  (0..99)
   DayOfWeek As Byte      // day of the week (1..7)
End Structure 

Dim Time As TTime,
    Date As TDate,
    Seconds_Poll As Byte 
   
Sub SetTime(Hour, Minute, Second, DayOfWeek, Day, Month, Year As Byte)
    
    I2C.Start
        I2C.WriteByte(%11010000)             // Send the RTC address, and put it in write mode
        I2C.WriteByte($00)                   // Move the pointer to first register
        I2C.WriteByte(DecToBCD(Second))      // Write each byte
        I2C.WriteByte(DecToBCD(Minute))      //
        I2C.WriteByte(DecToBCD(Hour))        //
        I2C.WriteByte(DecToBCD(DayOfWeek))   //
        I2C.WriteByte(DecToBCD(Day))         //
        I2C.WriteByte(DecToBCD(Month))       //
        I2C.WriteByte(DecToBCD(Year))        //
        I2C.WriteByte(0)                     //
    I2C.Stop    
    
End Sub

Sub GetTime()

    I2C.Start
        I2C.WriteByte(%11010000)
        I2C.WriteByte($00)
    I2C.Restart      
        I2C.WriteByte(%11010001)
        Time.Second = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))
        Time.Minute = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))
        Time.Hour = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))
        Date.DayOfWeek = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))
        Date.Day = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))
        Date.Month = BCDToDec(I2C.ReadByte(I2C_ACKNOWLEDGE))  
        Date.Year = BCDToDec(I2C.ReadByte(I2C_NOT_ACKNOWLEDGE))
    I2C.Stop 
    
End Sub


// Start Of Program...
SetAllDigital                             // Make all pins digital I/O's
I2C.Initialize()                          // Set up the I2C

DelayMS(150)
Cls

SetTime(03,42,00,07,06,05,07)

Main: 

    GetTime
         
    If Time.Second = Seconds_Poll Then 
        GoTo Main                         // If there is update in Secs, display time and Date
    EndIf
    
    // Display the new details on the LCD
    WriteAt(1,1,"Time: ", DecToStr(Time.Hour,2), ":", DecToStr(Time.Minute,2), ":", DecToStr(Time.Second,2))
    WriteAt(2,1,"Date: ", DecToStr(Date.Day,2), "-", DecToStr(Date.Month,2), "-", DecToStr(Date.Year,2))
    
    Seconds_Poll = Time.Second            // Update the seconds polling register
    
    GoTo Main

Where you can get the components;