Create digitally controlled oscillator with LTC6903 and PIC18F47K42
Timing perfection at your fingertips
Published May 27, 2023
Click board™
Clock Gen 5 Click
Dev. board
EasyPIC v8
Compiler
NECTO Studio
MCU
PIC18F47K42
Elevate performance and maximize efficiency by adding a clock generator to your solution
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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.
Features overview
Development board
EasyPIC v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports many high pin count 8-bit PIC microcontrollers from Microchip, regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer. 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, EasyPIC v8 provides a fluid and immersive working experience, allowing access anywhere and under any
circumstances at any time. Each part of the EasyPIC v8 development board contains the components necessary for the most efficient operation of the same board. In addition to the advanced integrated CODEGRIP programmer/debugger module, which offers many valuable programming/debugging options and seamless integration with the Mikroe software environment, the board 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 DEVICE, and CAN are also included, including the well-established mikroBUS™ standard, two display options (graphical and character-based LCD), and several different DIP sockets. These sockets cover a wide range of 8-bit PIC MCUs, from the smallest PIC MCU devices with only eight up to forty pins. EasyPIC 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.
Microcontroller Overview
MCU Card / MCU
Architecture
PIC
MCU Memory (KB)
128
Silicon Vendor
Microchip
Pin count
40
RAM (Bytes)
8192
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Click board™ Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the EasyPIC v8 as your development board.
Track your results in real time
Application Output
1. Application Output - In Debug mode, the 'Application Output' window enables real-time data monitoring, offering direct insight into execution results. Ensure proper data display by configuring the environment correctly using the provided tutorial.
2. UART Terminal - Use the UART Terminal to monitor data transmission via a USB to UART converter, allowing direct communication between the Click board™ and your development system. Configure the baud rate and other serial settings according to your project's requirements to ensure proper functionality. For step-by-step setup instructions, refer to the provided tutorial.
3. Plot Output - The Plot feature offers a powerful way to visualize real-time sensor data, enabling trend analysis, debugging, and comparison of multiple data points. To set it up correctly, follow the provided tutorial, which includes a step-by-step example of using the Plot feature to display Click board™ readings. To use the Plot feature in your code, use the function: plot(*insert_graph_name*, variable_name);. This is a general format, and it is up to the user to replace 'insert_graph_name' with the actual graph name and 'variable_name' with the parameter to be displayed.
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
The complete application code and a ready-to-use project are available through the NECTO Studio Package Manager for direct installation in the NECTO Studio. The application code can also be found on the MIKROE GitHub account.
/*!
* @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
