30 min

Redefine timekeeping for the modern age with PCF2123 and STM32L021K4

Time matters: Unleash the power of precision with our RTC solution

RTC 13 Click with UNI-DS v8

Published Feb 13, 2024

Click board™

RTC 13 Click

Dev Board



NECTO Studio



Elevate your engineering solutions with our advanced real-time clock, ensuring accurate time tracking and synchronization



Hardware Overview

How does it work?

RTC 13 Click is based on the PCF2123, an SPI configurable real-time clock/calendar optimized for low-power operations from NXP Semiconductors. It contains sixteen 8-bit registers with an auto-incrementing address counter, an on-chip 32.768kHz oscillator with two integrated load capacitors, a frequency divider that provides the source clock for the RTC, and a programmable clock output. The integrated oscillator ensures year, month, day, weekday, hours, minutes, and seconds, making this Click board™ suitable for various time-keeping applications such as high-duration timers, daily alarms, and more. The PCF2123 communicates with MCU using the standard SPI serial interface with a maximum

frequency of 8MHz, where data transfers serially with a maximum data rate of 6.25 Mbit/s. An alarm and timer function is also available, providing the possibility to generate a wake-up signal on an interrupt line, available on the INT pin of the mikroBUS™ socket and indicated by a red LED marked as INT. Besides, this Click board™ also has an onboard header labeled CLKOUT, which provides a programmable square-wave output clock signal controlled by one GPIO pin, a CLE pin routed to the RTS pin, the mikroBUS™ socket. Frequencies of 32.768kHz, representing a default value of 1Hz, can be generated and used as a system and MCU clock, input to a charge pump, or oscillator calibration. Like this one, the most

common RTC configuration is a battery-backed-up, which maintains time and continues its work without interruption during a power failure. That’s why, besides the PCF2123, the RTC 13 Click has a button cell battery holder compatible with the 3000TR battery holder, suitable for 12mm Coin Cell batteries. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.

RTC 13 Click top side image
RTC 13 Click bottom side image

Features overview

Development board

UNI-DS v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different STM32, Kinetis, TIVA, CEC, MSP, PIC, dsPIC, PIC32, and AVR MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, UNI-DS v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the UNI-DS v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector. Communication options such as USB-UART, USB

HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. UNI-DS v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

UNI-DS v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M0

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Clock Output Enable
SPI Chip Select
SPI Clock
Power Supply
Power Supply

Take a closer look


RTC 13 Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI-DS v8 as your development board.

Fusion for PIC v8 front image hardware assembly
Buck 22 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
v8 SiBRAIN MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for RTC 13 Click driver.

Key functions:

  • rtc13_get_time - RTC 13 get time function

  • rtc13_set_time - RTC 13 set time function

  • rtc13_get_date - RTC 13 get date function

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief RTC13 Click example
 * # Description
 * This is an example that demonstrates the use of the RTC 13 click board™.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initialization of SPI module, log UART and additional pins.
 * After driver initialization and default settings,
 * the app set the time to 23:59:50 and set the date to 04.08.2021.
 * ## Application Task
 * This is an example that shows the use of a RTC 13 click board™.
 * In this example, we read and display the current time and date, 
 * which we also previously set.
 * Results are being sent to the Usart Terminal where you can track their changes.
 * All data logs write on USB changes every 1 sec.
 * @author Nenad Filipovic

#include "board.h"
#include "log.h"
#include "rtc13.h"

static rtc13_t rtc13;
static log_t logger;

static uint8_t new_sec = 255;
static rtc13_time_t time;
static rtc13_date_t date;

void application_init ( void )
    log_cfg_t log_cfg;      /**< Logger config object. */
    rtc13_cfg_t rtc13_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.

    rtc13_cfg_setup( &rtc13_cfg );
    RTC13_MAP_MIKROBUS( rtc13_cfg, MIKROBUS_1 );
    err_t init_flag  = rtc13_init( &rtc13, &rtc13_cfg );
    if ( SPI_MASTER_ERROR == init_flag )
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );

    rtc13_default_cfg ( &rtc13 );
    log_info( &logger, " Application Task " );
    Delay_ms( 100 );
    date.weekday = 3; = 4;
    date.month = 8;
    date.year = 21;
    rtc13_set_date( &rtc13, date );
    Delay_ms( 100 );
    time.hours = 23;
    time.min = 59;
    time.sec = 50;
    rtc13_set_time( &rtc13, time );
    Delay_ms( 100 );

void application_task ( void )
    rtc13_get_time( &rtc13, &time );
    Delay_ms( 1 );
    rtc13_get_date( &rtc13, &date );
    Delay_ms( 1 );
    if ( time.sec != new_sec ) 
        log_printf( &logger, "  Date      : %.2d-%.2d-%.2d\r\n", ( uint16_t ), ( uint16_t ) date.month, ( uint16_t ) date.year );
        log_printf( &logger, "  Time      : %.2d:%.2d:%.2d\r\n", ( uint16_t ) time.hours, ( uint16_t ) time.min, ( uint16_t ) time.sec );
        log_printf( &logger, "- - - - - - - - - - - -\r\n" );
        new_sec = time.sec;
        Delay_ms( 1 );

void main ( void )
    application_init( );

    for ( ; ; )
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support