30 min

Create accurate square-wave pulses with LTC6904 and PIC18F25K80 for limitless possibilities

Timing perfected

Clock Gen 3 Click with Curiosity HPC

Published Jan 23, 2024

Click board™

Clock Gen 3 Click

Development board

Curiosity HPC


NECTO Studio



Unlock seamless synchronization and precise timing in your engineering projects with a powerful clock generator



Hardware Overview

How does it work?

Clock Gen 3 Click is based on the LTC6904 IC, 1kHz to 68MHz Serial Port Programmable Oscillator from Linear Technology. The LTC6904 is a low-power self-contained digital frequency source providing a precision frequency from 1KHz to 68MHz, set by the I2C interface operating up to 3.4 Mbps. This Click board™ features onboard I2C address jumpers, pull-up resistors, a power supply bypass capacitor, and a power LED. The maximum frequency error is 1.1% or 1.6% when operating with a flexible power supply voltage range from 2.7V to 5V, which makes it suitable for 3.3V and 5V MCUs. In most frequency ranges, the output of the Clock Gen 3 Click is generated as a division of the higher internal clock frequency. This helps to minimize jitter and subharmonics at the output of the device.

In the highest frequency ranges, the division ratio is reduced, which will result in a greater cycle-to-cycle jitter as well as spurs at the internal sampling frequency. Because the internal control loop runs at 1MHz to 2MHz without regard to the output frequency, output spurs separated from the set frequency by 1MHz to 2MHz may be observed. These spurs are characteristically more than 30dB below the level of the set frequency. The LTC6904 communicates with the MCU using the standard I2C 2-wire interface. The two bus lines, SDA and SCL, must be HIGH when the bus is not in use. If the I2C interface is not driven with a standard I2C compatible device, care must be taken to ensure that the SDA line is released during the ACK cycle to prevent bus contention.

The LTC6904 can respond to one of two 7-bit addresses. The first 6 bits (MSBs) have been factory programmed to 001011. The address pin, ADR (Pin 4), is programmed by the user and determines the LSB of the slave address, and it can be selected by an onboard SMD jumper labeled as ADD SEL, allowing selection of the slave address LSB. 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 3 Click top side image
Clock Gen 3 Click lateral side image
Clock Gen 3 Click bottom side image

Features overview

Development board

Curiosity HPC, standing for Curiosity High Pin Count (HPC) development board, supports 28- and 40-pin 8-bit PIC MCUs specially designed by Microchip for the needs of rapid development of embedded applications. This board has two unique PDIP sockets, surrounded by dual-row expansion headers, allowing connectivity to all pins on the populated PIC MCUs. It also contains a powerful onboard PICkit™ (PKOB), eliminating the need for an external programming/debugging tool, two mikroBUS™ sockets for Click board™ connectivity, a USB connector, a set of indicator LEDs, push button switches and a variable potentiometer. All

these features allow you to combine the strength of Microchip and Mikroe and create custom electronic solutions more efficiently than ever. Each part of the Curiosity HPC development board contains the components necessary for the most efficient operation of the same board. An integrated onboard PICkit™ (PKOB) allows low-voltage programming and in-circuit debugging for all supported devices. When used with the MPLAB® X Integrated Development Environment (IDE, version 3.0 or higher) or MPLAB® Xpress IDE, in-circuit debugging allows users to run, modify, and troubleshoot their custom software and hardware

quickly without the need for additional debugging tools. Besides, it includes a clean and regulated power supply block for the development board via the USB Micro-B connector, alongside all communication methods that mikroBUS™ itself supports. Curiosity HPC development board allows you to create a new application in just a few steps. Natively supported by Microchip software tools, it covers many aspects of prototyping thanks to many number of different Click boards™ (over a thousand boards), the number of which is growing daily.

Curiosity HPC double image

Microcontroller Overview

MCU Card / MCU




MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Output Enable
Power Supply
I2C Clock
I2C Data
Power Supply

Take a closer look


Clock Gen 3 Click Schematic schematic

Step by step

Project assembly

Curiosity HPC front no-mcu image hardware assembly

Start by selecting your development board and Click board™. Begin with the Curiosity HPC as your development board.

Curiosity HPC front no-mcu image hardware assembly
LTE Cat.1 2 Click front image hardware assembly
MCU DIP 28 hardware assembly
Prog-cut hardware assembly
LTE Cat.1 2 Click complete accessories setup image hardware assembly
Curiosity HPC Access 28pin-DIP - 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 DIP 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 3 Click driver.

Key functions:

  • void clockgen3_set_freq( float freq ) - Sets Frequency
  • void clockgen3_config( uint8_t cfg ) - Configuration

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 
 * \brief ClockGen3 Click example
 * # Description
 * This example demonstrates the use of Clock Gen 3 click board.
 * The demo application is composed of two sections :
 * ## Application Init 
 * Initializes the driver and configures the click board.
 * ## Application Task  
 * Sets different frequencies every 3 seconds and displays the set frequency 
 * on the USB UART.
 * \author MikroE Team
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "clockgen3.h"

// ------------------------------------------------------------------ VARIABLES

static clockgen3_t clockgen3;
static log_t logger;

// ------------------------------------------------------ APPLICATION FUNCTIONS

void application_init ( void )
    log_cfg_t log_cfg;
    clockgen3_cfg_t cfg;

     * 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.

    clockgen3_cfg_setup( &cfg );
    clockgen3_init( &clockgen3, &cfg );

    clockgen3_config( &clockgen3, CLOCKGEN3_CFG_ON_CLK_180 );
    Delay_ms( 500 );

void application_task ( void )
    log_printf( &logger, ">> Set Freq = 12.000 MHz \r\n" );
    clockgen3_set_freq( &clockgen3, 12000.0 );
    Delay_ms( 3000 );
    log_printf( &logger, ">> Set Freq = 8.000 MHz \r\n" );
    clockgen3_set_freq( &clockgen3, 8000.0 );
    Delay_ms( 3000 );
    log_printf( &logger, ">> Set Freq = 5.500 MHz \r\n" );
    clockgen3_set_freq( &clockgen3, 5500.0 );
    Delay_ms( 3000 );
    log_printf( &logger, ">> Set Freq = 2.700 MHz \r\n" );
    clockgen3_set_freq( &clockgen3, 2700.0 );
    Delay_ms( 3000 );
    log_printf( &logger, ">> Set Freq = 800 KHz \r\n" );
    clockgen3_set_freq( &clockgen3, 800.0 );
    Delay_ms( 3000 );
    log_printf( &logger, ">> Set Freq = 200 KHz \r\n" );
    clockgen3_set_freq( &clockgen3, 200.0 );
    Delay_ms( 3000 );
    log_printf( &logger, "---------------------------- \r\n" );

void main ( void )
    application_init( );

    for ( ; ; )
        application_task( );

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

Additional Support