30 min

Create digitally controlled oscillator with LTC6903 and STM32L4S5ZI

Timing perfection at your fingertips

Clock Gen 5 Click with UNI Clicker

Published May 27, 2023

Click board™

Clock Gen 5 Click

Development board

UNI Clicker


NECTO Studio



Elevate performance and maximize efficiency by adding a clock generator to your solution



Hardware Overview

How does it work?

Clock Gen 5 Click is based on the LTC6903, a low-power self-contained digital frequency source providing a precision frequency from 1kHz to 68MHz set through a 3-wire digital interface from Analog Devices. The LTC6903 contains an internal feedback loop that controls a high-frequency square wave (VCO) operating between 34MHz and 68MHz. It is also a resistor-controlled oscillator that offers an integrated serial resistor DAC and a set of digital frequency dividers. The oscillator frequency is inversely proportional to the resistance of the DAC, where step size ranges between 0.05% and 0.1% of the frequency. In most frequency ranges, the output of the Clock Gen 5 Click is generated as a division of the higher internal clock

frequency. This helps to minimize jitter and sub-harmonics at the output of the device. In the highest frequency ranges, the division ratio is reduced, which will result in greater cycle-to-cycle jitter as well as spurs at the internal sampling frequency. The output clock signals, available on the SMA connectors with an impedance of 50Ω labeled as MAIN and AUX CLOCK, are primarily conducted through the TC7SZ125FU, a 3-state bus buffer before outputting allowing the LTC6903 to operate normally, producing the required output. Clock Gen 5 Click communicates with MCU using the 3-Wire SPI serial interface and operates at a clock frequency of up to 20 MHz. The output signals are controlled by the register bits MODE1 and MODE0,

where the outputs can be disabled through these bits. When both output signals are disabled through the mode control bits, the internal oscillator is also disabled. The OE pin routed on the RST pin of the mikroBUS™ socket can also be used to asynchronously disable either output without shutting down the oscillator entirely. 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. However, the 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.

Clock Gen 5 Click top side image
Clock Gen 5 Click lateral side image
Clock Gen 5 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-M4

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Asynchronous Enable
SPI Chip Select
SPI Clock
Power Supply
Power Supply

Take a closer look


Clock Gen 5 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
GNSS2 Click front image hardware assembly
SiBRAIN for STM32F745VG front image hardware assembly
Prog-cut hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
UNI Clicker Access 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 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 Clock Gen 5 Click driver.

Key functions:

  • void clockgen5_out_enable ( uint8_t en_out ) - Enable output function.
  • void clockgen5_set_config ( uint8_t cfg ) - Set configuration function.
  • void clockgen5_set_freq ( float freq ) - Set frequency 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 ClockGen5 Click example
 * # Description
 * This is an example that demonstrates the use of the Clock Gen 5 click board.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initialization driver enables - SPI,
 * set output configuration CLK 180, also write log.
 * ## Application Task
 * In this example, we adjusts different frequencies every 3 sec.
 * Results are being sent to the Uart Terminal where you can track their changes.
 * @author Stefan Ilic

#include "board.h"
#include "log.h"
#include "clockgen5.h"

static clockgen5_t clockgen5;
static log_t logger;

void application_init ( void ) {
    log_cfg_t log_cfg;  /**< Logger config object. */
    clockgen5_cfg_t clockgen5_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.

    clockgen5_cfg_setup( &clockgen5_cfg );
    CLOCKGEN5_MAP_MIKROBUS( clockgen5_cfg, MIKROBUS_1 );
    err_t init_flag  = clockgen5_init( &clockgen5, &clockgen5_cfg );
    if ( SPI_MASTER_ERROR == init_flag ) {
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... %d", init_flag );

        for ( ; ; );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "    Enabling Output   \r\n" );
    clockgen5_out_enable( &clockgen5, CLOCKGEN5_OUTPUT_ENABLE);
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "   Set configuration   \r\n" );
    log_printf( &logger, "-----------------------\r\n" );
    clockgen5_set_config( &clockgen5, CLOCKGEN5_CFG_ON_CLK_180 );
    Delay_ms( 500 );
    log_info( &logger, " Application Task " );

void application_task ( void ) {
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "        12.0 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 12000.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "         8.0 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 8000.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "         5.5 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 5500.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "         2.7 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 2700.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "         0.8 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 800.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "-----------------------\r\n" );
    log_printf( &logger, "         0.2 MHz       \r\n" );
    clockgen5_set_freq( &clockgen5, 200.0 );
    Delay_ms( 3000 );

void main ( void ) {
    application_init( );

    for ( ; ; ) {
        application_task( );

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

Additional Support