30 min

Redefine timekeeping for the modern age with PCF2123 and STM32F756ZG

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

RTC 13 Click with UNI Clicker

Published Oct 21, 2023

Click board™

RTC 13 Click

Development board

UNI Clicker


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 Clicker is a compact development board designed as a complete solution that brings the flexibility of add-on Click boards™ to your favorite microcontroller, making it a perfect starter kit for implementing your ideas. It supports a wide range of microcontrollers, such as different ARM, PIC32, dsPIC, PIC, and AVR from various vendors like Microchip, ST, NXP, and TI (regardless of their number of pins), four mikroBUS™ sockets for Click board™ connectivity, a USB connector, LED indicators, buttons, a debugger/programmer connector, and two 26-pin headers for interfacing with external electronics. Thanks to innovative manufacturing technology, it allows you to build

gadgets with unique functionalities and features quickly. Each part of the UNI Clicker development kit contains the components necessary for the most efficient operation of the same board. In addition to the possibility of choosing the UNI Clicker programming method, using a third-party programmer or CODEGRIP/mikroProg connected to onboard JTAG/SWD header, the UNI Clicker board also includes a clean and regulated power supply module for the development kit. It provides two ways of board-powering; through the USB Type-C (USB-C) connector, where onboard voltage regulators provide the appropriate voltage levels to each component on the board, or using a Li-Po/Li

Ion battery via an onboard battery connector. All communication methods that mikroBUS™ itself supports are on this board (plus USB HOST/DEVICE), including the well-established mikroBUS™ socket, a standardized socket for the MCU card (SiBRAIN standard), and several user-configurable buttons and LED indicators. UNI Clicker is an integral part of the Mikroe ecosystem, allowing you to create a new application in minutes. Natively supported by Mikroe software tools, it covers many aspects of prototyping thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

UNI clicker double image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M7

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

UNI Clicker front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI Clicker as your development board.

UNI Clicker front image hardware assembly
Thermo 28 Click front image hardware assembly
SiBRAIN for STM32F745VG front image hardware assembly
Prog-cut hardware assembly
UNI Clicker MB 1 - upright/with-background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
Necto image step 5 hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto No Display image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Debug Image Necto Step hardware assembly

Track your results in real time

Application Output

After loading the code example, pressing the "DEBUG" button builds and programs it on the selected setup.

Application Output Step 1

After programming is completed, a header with buttons for various actions available in the IDE appears. By clicking the green "PLAY "button, we start reading the results achieved with Click board™.

Application Output Step 3

Upon completion of programming, the Application Output tab is automatically opened, where the achieved result can be read. In case of an inability to perform the Debug function, check if a proper connection between the MCU used by the setup and the CODEGRIP programmer has been established. A detailed explanation of the CODEGRIP-board connection can be found in the CODEGRIP User Manual. Please find it in the RESOURCES section.

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