In this tutorial we will be discussing about the internal RTC of LPC1768. We will see what are the different registers associated with the RTC but we will mainly focus on basics registers required to use RTC. Later we will see how to use Explore Embedded library for RTC.

1 RTC Registers
2 RTC Register Configuration
3 Steps for Using RTC
4 Code Example
- 4.1 Example 1
- 4.2 Using Explore Embedded Libraries
5 Connection
6 Downloads

RTC Registers

The RTC includes a number of registers. We will concentrate some of the basic required registers.

Register	Description
CCR	Clock Control Register
Consolidated Time Registers
CTIME 0	Consolidated Time Register 0
CTIME 1	Consolidated Time Register 1
CTIME 2	Consolidated Time Register 2
Time Counter Registers
SEC	Seconds Counter
MIN	Minutes Register
HOUR	Hours Register
DOM	Day of Month Register
DOW	Day of Week Register
DOY	Day of Year Register
MONTH	Months Register
YEAR	Years Register
CALIBRATION	Calibration value Register

RTC Register Configuration

Lets see how to configure these registers.

CCR
31:5	4	3:2	1	0
-	CCALEN	-	CTCRST	CLKEN

CCR ( Clock Control Register )

The Clock Control Register register controls the operation of the clock divide circuit.

Bit 0 – CLKEN : Clock Enable
This bit is written with one to enable time counters and written with zero to disable time counters.

Bit 1 - CTCRST : CTC Reset
When this bit is set to one, the internal oscillator divider are reset.

Bit 3:2 - Reserved
These bits must be set to zero for normal RTC operation.

Bit 4 - CCALEN : Calibration counter enable
To disable calibration counter and reset it to zero, write one to this bit. When written zero, the counter is enabled and starts counting

Bit 31:5 - Reserved

Time Counter Register

The time value consists of the eight counters and there is separate register associated with each counter. To update the RTC, new values should be written to these registers.

Time Counter Registers
Register	Description	Minimum Value	Maximum Value
SEC	Seconds value	0	59
MIN	Minutes value	0	59
HOUR	Hours value	0	23
DOM	Day of Month value	1	28,29,30 or 31(depending on the month)
DOW	Day of Week value	0	6
DOY	Day of Year value	1	365 (366 for Leap Year)
MONTH	Month value	1	12
YEAR	Year value	0	4095

Consolidated Time Registers

The values of the Time Counters can optionally be read in a consolidated format which allows the programmer to read all time counters with only three read operations.

There are 3 Consolidated Time Registers. The minimum and maximum values of the various fields in these registers are same as the respective Time Counter Register.

These registers are read only. New values should be written to Time Counter Registers.

Consolidated Time Register 0 ( CTIME0 )
31:27	26:24	23:21	20:16	15:14	13:8	7:6	5:0
Reserved	Day of Week	Reserved	Hours	Reserved	Minute	Reserved	Second

Consolidated Time Register 1 ( CTIME1 )
31:27	27:16	15:12	11:8	7:5	4:0
Reserved	Year	Reserved	Month	Reserved	Day of Month

Consolidated Time Register 2 ( CTIME2 )
31:12	11:0
Reserved	Day of Year

Steps for Using RTC

Initialize RTC

Disable RTC clock using CCR ( Clock Control Register )
Reset clock using CCR register
Enable RTC calibration in RTC Calibration Register
Enable the clock for RTC using CCR register

Set Date and Time

As we saw previously, there are separate Time Counter registers for each time parameter hour, min, sec and same is the case date. We just need to copy the required values to these registers.

Read Date and Time

The values of date and time can be read from associated Time Counter registers. Alternately, date and time can also be read from Consolidated Time registers.

We will use Time Counter registers for both reading and writing.

Code Example

Example 1

In this example we will see how to use lpc1768 inbuilt RTC. The time and date will be displayed continuously on 2x16 LCD.

	#include <lpc17xx.h> //Device specific header file
	#include "lcd.h" // Explore Embedded LCD library

	/* bit position of CCR register */
	#define SBIT_CLKEN 0 /* RTC Clock Enable*/
	#define SBIT_CTCRST 1 /* RTC Clock Reset */
	#define SBIT_CCALEN 4 /* RTC Calibration counter enable */


	int main()
	{
	uint16_t year;
	uint8_t hour, min, sec, date, month;

	SystemInit(); //Clock and PLL configuration

	/* Setup/Map the controller pins for LCD operation
	RS RW EN D0 D1 D2 D3 D4 D5 D6 D7 (P_NC: Not Connected)*/
	LCD_SetUp(P2_0,P2_1,P2_2,P_NC,P_NC,P_NC,P_NC,P1_24,P1_25,P1_26,P1_27);

	/* Specify the LCD type(2x16) for initialization*/
	LCD_Init(2,16);

	/* Disable RTC clock, reset clock, Enable RTC calibration */
	LPC_RTC->CCR = ((1 << SBIT_CTCRST ) \| (1 << SBIT_CCALEN));
	LPC_RTC->CALIBRATION = 0x00;
	LPC_RTC->CCR = (1 << SBIT_CLKEN); /* Enable the clock for RTC */

	/* Set Date and Time only once, comment these lines after setting the time and date */
	// Set Date 14th Nov 2015
	LPC_RTC->DOM = 14; // Update date value
	LPC_RTC->MONTH = 11; // Update month value
	LPC_RTC->YEAR = 2015; // Update year value

	// Set Time 10:40:25 AM
	LPC_RTC->HOUR = 10; // Update hour value
	LPC_RTC->MIN = 40; // Update min value
	LPC_RTC->SEC = 25; // Update sec value


	while (1)
	{
	/* Read Time */
	hour = LPC_RTC->HOUR;
	min = LPC_RTC->MIN;
	sec = LPC_RTC->SEC;

	/* Read Date */
	date = LPC_RTC->DOM;
	month = LPC_RTC->MONTH;
	year = LPC_RTC->YEAR;

	/* Display date and time on LCD */
	LCD_GoToLine(0); /* Go to First line of 2x16 LCD */
	LCD_Printf("Time: %2d:%2d:%2d",hour,min,sec);
	LCD_GoToLine(1); /* Go to Second line of 2x16 LCD */
	LCD_Printf("Date: %2d/%2d/%4u",date,month,year);
	}
	}

view raw lpc1768_RTC_Example1.c hosted with ❤ by GitHub

Using Explore Embedded Libraries

Now we will discuss how to use Explore Embedded Libraries for LPC1768 inbuilt RTC. Refer the LCD tutorial for interfacing the 2x16 lcd.

	#include <LPC17xx.h>
	#include "rtc.h"
	#include "lcd.h"

	int main()
	{
	rtc_t rtc;

	SystemInit();

	/Connect RS RW EN D0 D1 D2 D3 D4 D5 D6 D7 (P_NC: Not Connected)/
	LCD_SetUp(P2_0,P2_1,P2_2,P_NC,P_NC,P_NC,P_NC,P1_24,P1_25,P1_26,P1_27);
	LCD_Init(2,16);

	RTC_Init();

	rtc.hour = 10; // 10:40:20 am
	rtc.min = 40;
	rtc.sec = 0;

	rtc.date = 1; //1st Jan 2016
	rtc.month = 1;
	rtc.year = 2016;
	rtc.weekDay = 5; // Friday: 5th day of week considering monday as first day.


	/*##### Set the time and Date only once. Once the Time and Date is set, comment these lines
	and reflash the code. Else the time will be set every time the controller is reset*/
	RTC_SetDateTime(&rtc); // 10:40:20 am, 1st Jan 2016


	/* Display the Time and Date continuously */
	while(1)
	{
	RTC_GetDateTime(&rtc);
	LCD_GoToLine(0);
	LCD_Printf("time:%2d:%2d:%2d \nDate:%2d/%2d/%4d",(uint16_t)rtc.hour,(uint16_t)rtc.min,(uint16_t)rtc.sec,(uint16_t)rtc.date,(uint16_t)rtc.month,(uint16_t)rtc.year);
	}
	}