This post shows how to make a real time clock and calendar using PIC16F84 and DS3231 RTC.
The DS3231 uses I2C protocol to interface with the master device which is in this example the PIC16F84A MCU. In this project software I2C is used because the PIC16F84A MCU has no hardware I2C module.
- PIC16F84A microcontroller
- 1602 LCD screen
- 8MHz crystal oscillator
- 2 x 22pF ceramic capacitor
- 10K ohm variable resistor
- 3 x 10K ohm resistor
- 2 x push button
- 5V supply source
- Jumper wires
DS3231 board contains the following components:
- DS3231 RTC – datasheet
- 2 x 4.7K ohm resistors
- 0.1uF ceramic capacitor
- 3V coin cell battery
Interfacing PIC16F84 with DS3231 RTC circuit:
Interfacing PIC16F84 with DS3231 RTC C code:
The C code below was tested with CCS PIC C compiler version 5.051.
I used the function below to initialize the software I2C where pin RA0 and pin RA1 are used for SDA and SCL lines respectively (PIC16F84A is used as master device):
#use I2C(MASTER, SDA=PIN_A0, SCL=PIN_A1, FAST=100000)
The DS3231 works with BCD format only and to convert the BCD to decimal and vise versa I used the 2 functions below. Before displaying (after reading from DS3231), the data have to be converted from BCD to decimal, and before writing to the DS3231 (after editing the parameters) the data have to be converted from decimal to BCD:
Each function returns the converted value of the variable number.
void DS3231_display() : displays time and calendar data, before displaying time and calendar data are converted from BCD format to decimal format using the function bcd_to_decimal(number) .
int8 edit(x, y, parameter) : I used this function to edit time calendar parameters (minutes, hours, date, month and year). I used a variable named i to distinguish between the parameters:
i = 0, 1 : time hours and minutes respectively
i = 2, 3, 4: calendar date, month and year respectively
After the edit of time and calendar, the data have to be converted back to BCD format using the function decimal_to_bcd(number) and written to the DS3231.
void blink() : this small function works as a delay except that it is interrupted by the buttons B1 (connected to RA2) and B2 (connected to RA3). When called and without pressing any button the total time is 10 x 25ms = 250ms. With this function we can see the blinking of the selected parameter with a frequency of 2Hz. So a delay of 250ms comes after the print of the selected parameter and after that delay a 2 spaces is printed which makes the parameter disappears from the LCD and another 250ms delay comes after the print of the 2 spaces.