Intermediate
30 min

Create complex waveforms with AD9106 and STM32F091RC

Rock the Waves

Waveform 4 Click with Nucleo-64 with STM32F091RC MCU

Published Feb 26, 2024

Click board™

Waveform 4 Click

Dev Board

Nucleo-64 with STM32F091RC MCU

Compiler

NECTO Studio

MCU

STM32F091RC

Unleash your creativity with a cutting-edge waveform generator

A

A

Hardware Overview

How does it work?

Waveform 4 Click is based on the AD9106, a high-performance, quad digital-to-analog converter (DAC) integrating on-chip pattern memory for complex waveform generation with a direct digital synthesizer (DDS) from Analog Devices. The DDS is a 12-bit output, up to 180 MHz master clock sinewave generator with a 24-bit tuning word allowing 10.8 Hz/LSB frequency resolution. This Click board™, by default, uses an onboard 125 MHz crystal oscillator as a clock source, which is also the maximum output frequency for this board. The high-speed, high-dynamic-range, multichannel complex waveforms generated by AD9106 are suitable for applications such as ultrasound transducer excitation, medical instrumentation, portable instrumentation, signal generators, and arbitrary waveform generators. Pattern data can include directly generated SRAM-stored waveforms, DDS outputs amplitude-modulated by SRAM, or DDS frequency tuning words from SRAM providing chirp or frequency shift keying (FSK) modulation. An internal pattern-control state machine allows the user to program the pattern period for all D/A converters, the start delay within the pattern period for the signal

output on each D/A converter channel, and the repetition rate of the pattern. The generation of a pattern is configurable via TRG routed to the PWM pin of the mikroBUS™ socket. A falling edge on the TRG pin starts generating a pattern, while the rising edge represents a request to terminate pattern generation. The AD9106 has a single frequency output and independently programmable phase shift outputs for each of the four integrated DACs. Besides, gain adjustment factors and offset adjustments are applied to the digital signals on their way into the four DACs. The two DAC outputs of the AD9106 are filtered by an RC network and then amplified via ADA4817-2, an operational amplifier that combines new architecture for FET input operational amplifiers with the eXFCB process from Analog Devices, resulting in an outstanding combination of speed and low noise. The other two outputs, without amplification, were routed on onboard headers labeled as I2 and I4. In addition to the positive supply voltage requirement, the ADA4817-2 amplifier also has a negative supply voltage, achieved by the ADM8829, a charge-pump voltage inverter used to generate a negative supply from a positive input

from Analog Devices. The output signal from the ADA4817-2 follows two paths. One path is routed to an output connector labeled OUT1, while the other is routed to an output connector labeled OUT3. On these connectors, the AD9106 can generate two types of signal patterns under the control of its programmable pattern generator: periodic pulse train waveforms that repeat indefinitely or periodic pulse train waveforms that repeat a finite number of times. This Click board™ communicates with MCU through a standard SPI interface to program the internal registers for complete control of the AD9106. Besides, it possesses additional functionality, such as a reset function implemented and routed at the RST pin of the mikroBUS™ socket, which resets all registers of the AD9106 to their default state. This Click board™ can only be operated with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. However, the Click board™ comes equipped with a library containing functions and an example code that can be used as a reference for further development.

waveform-4-click-hardware-overview

Features overview

Development board

Nucleo-64 with STM32F091RC MCU offers a cost-effective and adaptable platform for developers to explore new ideas and prototype their designs. This board harnesses the versatility of the STM32 microcontroller, enabling users to select the optimal balance of performance and power consumption for their projects. It accommodates the STM32 microcontroller in the LQFP64 package and includes essential components such as a user LED, which doubles as an ARDUINO® signal, alongside user and reset push-buttons, and a 32.768kHz crystal oscillator for precise timing operations. Designed with expansion and flexibility in mind, the Nucleo-64 board features an ARDUINO® Uno V3 expansion connector and ST morpho extension pin

headers, granting complete access to the STM32's I/Os for comprehensive project integration. Power supply options are adaptable, supporting ST-LINK USB VBUS or external power sources, ensuring adaptability in various development environments. The board also has an on-board ST-LINK debugger/programmer with USB re-enumeration capability, simplifying the programming and debugging process. Moreover, the board is designed to simplify advanced development with its external SMPS for efficient Vcore logic supply, support for USB Device full speed or USB SNK/UFP full speed, and built-in cryptographic features, enhancing both the power efficiency and security of projects. Additional connectivity is

provided through dedicated connectors for external SMPS experimentation, a USB connector for the ST-LINK, and a MIPI® debug connector, expanding the possibilities for hardware interfacing and experimentation. Developers will find extensive support through comprehensive free software libraries and examples, courtesy of the STM32Cube MCU Package. This, combined with compatibility with a wide array of Integrated Development Environments (IDEs), including IAR Embedded Workbench®, MDK-ARM, and STM32CubeIDE, ensures a smooth and efficient development experience, allowing users to fully leverage the capabilities of the Nucleo-64 board in their projects.

Nucleo 64 with STM32F091RC MCU double side image

Microcontroller Overview

MCU Card / MCU

default

Architecture

ARM Cortex-M0

MCU Memory (KB)

256

Silicon Vendor

STMicroelectronics

Pin count

64

RAM (Bytes)

32768

You complete me!

Accessories

Click Shield for Nucleo-64 comes equipped with two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the STM32 Nucleo-64 board with no effort. This way, Mikroe allows its users to add any functionality from our ever-growing range of Click boards™, such as WiFi, GSM, GPS, Bluetooth, ZigBee, environmental sensors, LEDs, speech recognition, motor control, movement sensors, and many more. More than 1537 Click boards™, which can be stacked and integrated, are at your disposal. The STM32 Nucleo-64 boards are based on the microcontrollers in 64-pin packages, a 32-bit MCU with an ARM Cortex M4 processor operating at 84MHz, 512Kb Flash, and 96KB SRAM, divided into two regions where the top section represents the ST-Link/V2 debugger and programmer while the bottom section of the board is an actual development board. These boards are controlled and powered conveniently through a USB connection to program and efficiently debug the Nucleo-64 board out of the box, with an additional USB cable connected to the USB mini port on the board. Most of the STM32 microcontroller pins are brought to the IO pins on the left and right edge of the board, which are then connected to two existing mikroBUS™ sockets. This Click Shield also has several switches that perform functions such as selecting the logic levels of analog signals on mikroBUS™ sockets and selecting logic voltage levels of the mikroBUS™ sockets themselves. Besides, the user is offered the possibility of using any Click board™ with the help of existing bidirectional level-shifting voltage translators, regardless of whether the Click board™ operates at a 3.3V or 5V logic voltage level. Once you connect the STM32 Nucleo-64 board with our Click Shield for Nucleo-64, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.

Click Shield for Nucleo-64 accessories 1 image

Used MCU Pins

mikroBUS™ mapper

NC
NC
AN
Reset
PC12
RST
SPI Chip Select
PB12
CS
SPI Clock
PB3
SCK
SPI Data OUT
PB4
MISO
SPI Data IN
PB5
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
Pattern Trigger
PC8
PWM
NC
NC
INT
NC
NC
TX
NC
NC
RX
NC
NC
SCL
NC
NC
SDA
NC
NC
5V
Ground
GND
GND
1

Take a closer look

Click board™ Schematic

Waveform 4 Click Schematic schematic

Step by step

Project assembly

Click Shield for Nucleo-64 accessories 1 image hardware assembly

Start by selecting your development board and Click board™. Begin with the Nucleo-64 with STM32F091RC MCU as your development board.

Click Shield for Nucleo-64 accessories 1 image hardware assembly
Nucleo 64 with STM32F401RE MCU front image hardware assembly
LTE IoT 5 Click front image hardware assembly
Prog-cut hardware assembly
LTE IoT 5 Click complete accessories setup image hardware assembly
Nucleo-64 with STM32XXX MCU Access MB 1 Mini B Conn - 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
Clicker 4 for STM32F4 HA MCU Step 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 via Debug Mode

1. Once the code example is loaded, pressing the "DEBUG" button initiates the build process, programs it on the created setup, and enters Debug mode.

2. After the programming is completed, a header with buttons for various actions within the IDE becomes visible. Clicking the green "PLAY" button starts reading the results achieved with the Click board™. The achieved results are displayed in the Application Output tab.

DEBUG_Application_Output

Software Support

Library Description

This library contains API for Waveform 4 Click driver.

Key functions:

  • waveform4_set_frequency This function sets the sine and cosine (DDS) waves output frequency.

  • waveform4_set_gain This function sets the gain level of a desired channel.

  • waveform4_set_wave_output This function sets a desired output signal wave to the selected channel.

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 Waveform4 Click example
 *
 * # Description
 * This example demonstrates the use of Waveform 4 click board.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes the driver and performs the click default configuration which
 * resets the registers and sets the sine wave output with default gain and 
 * default frequency for all channels. After that it displays the list of
 * supported commands on the USB UART.
 *
 * ## Application Task
 * Depending on the command character received from USB UART it changes the 
 * signal frequency, gain or wave of the selected channel.
 *
 * @author Stefan Filipovic
 *
 */

#include "board.h"
#include "log.h"
#include "waveform4.h"

static waveform4_t waveform4;
static log_t logger;

#define GAIN_STEP 0.05  // Gain step, used for increase/decrease gain commands.
#define FREQ_STEP 100   // Frequency step, used for increase/decrease frequency commands.

uint32_t freq = WAVEFORM4_DEFAULT_FREQUENCY;
float gain = WAVEFORM4_DEFAULT_GAIN;
uint8_t channel = WAVEFORM4_CHANNEL_1;
uint8_t wave = WAVEFORM4_WAVE_SINE;

/**
 * @brief Waveform 4 display commands function.
 * @details This function displays the list of supported commands on the USB UART.
 * @return None.
 * @note None.
 */
void waveform4_display_commands ( void );

/**
 * @brief Waveform 4 parse command function.
 * @details This function checks if the input command is supported and executes it.
 * @param[in] command : Command input, for more details refer to @b waveform4_display_commands function.
 * @return @li @c  0 - Success,
 *         @li @c -1 - Wrong command or command is not executed properly.
 *
 * See #err_t definition for detailed explanation.
 * @note None.
 */
err_t waveform4_parse_command ( uint8_t command );

void application_init ( void )
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    waveform4_cfg_t waveform4_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.
    waveform4_cfg_setup( &waveform4_cfg );
    WAVEFORM4_MAP_MIKROBUS( waveform4_cfg, MIKROBUS_1 );
    if ( SPI_MASTER_ERROR == waveform4_init( &waveform4, &waveform4_cfg ) )
    {
        log_error( &logger, " Communication init." );
        for ( ; ; );
    }
    
    if ( WAVEFORM4_ERROR == waveform4_default_cfg ( &waveform4 ) )
    {
        log_error( &logger, " Default configuration." );
        for ( ; ; );
    }
    
    waveform4_display_commands ( );
    log_info( &logger, " Application Task " );
}

void application_task ( void )
{
    uint8_t command = 0;
    if ( log_read ( &logger, &command, 1 ) > 0 ) 
    {
        waveform4_parse_command ( command );
    }
}

int main ( void ) 
{
    /* Do not remove this line or clock might not be set correctly. */
    #ifdef PREINIT_SUPPORTED
    preinit();
    #endif
    
    application_init( );
    
    for ( ; ; ) 
    {
        application_task( );
    }

    return 0;
}

void waveform4_display_commands ( void )
{
    log_printf( &logger, "-------------------------------------------\r\n" );
    log_info( &logger, "- UART commands list -\r\n" );
    log_printf( &logger, "'+' - Increase frequency.\r\n" );
    log_printf( &logger, "'-' - Decrease frequency.\r\n" );
    log_printf( &logger, "'G' - Increase gain.\r\n" );
    log_printf( &logger, "'g' - Decrease gain.\r\n" );
    log_printf( &logger, "'S' or 's' - Select sine wave output.\r\n" );
    log_printf( &logger, "'C' or 'c' - Select cosine wave output.\r\n" );
    log_printf( &logger, "'T' or 't' - Select triangle wave output.\r\n" );
    log_printf( &logger, "'P' or 'p' - Select positive sawtooth wave output.\r\n" );
    log_printf( &logger, "'N' or 'n' - Select negative sawtooth wave output.\r\n" );
    log_printf( &logger, "'1' - Select channel 1.\r\n" );
    log_printf( &logger, "'2' - Select channel 2.\r\n" );
    log_printf( &logger, "'3' - Select channel 3.\r\n" );
    log_printf( &logger, "'4' - Select channel 4.\r\n" );
    log_printf( &logger, "'L' or 'l' - Display commands list.\r\n" );
    log_printf( &logger, "-------------------------------------------\r\n" );
}

err_t waveform4_parse_command ( uint8_t command )
{
    switch( command )
    {
        case '+': 
        {
            freq += FREQ_STEP;
            if ( freq > WAVEFORM4_MASTER_CLOCK )
            {
                freq = WAVEFORM4_MASTER_CLOCK;
            }
            log_printf( &logger, "Frequency increased: %lu Hz\r\n", freq );
            return waveform4_set_frequency ( &waveform4, freq );
        }
        case '-': 
        {
            freq -= FREQ_STEP;
            if ( freq > WAVEFORM4_MASTER_CLOCK )
            {
                freq = 0;
            }
            log_printf( &logger, "Frequency decreased: %lu Hz\r\n", freq );
            return waveform4_set_frequency ( &waveform4, freq );
        }
        case 'G': 
        {
            gain += GAIN_STEP;
            if ( gain > WAVEFORM4_GAIN_MAX )
            {
                gain = WAVEFORM4_GAIN_MAX;
            }
            log_printf( &logger, "Gain increased: %.3f\r\n", gain );
            return waveform4_set_gain ( &waveform4, channel, gain );
        }
        case 'g': 
        {
            gain -= GAIN_STEP;
            if ( gain < WAVEFORM4_GAIN_MIN )
            {
                gain = WAVEFORM4_GAIN_MIN;
            }
            log_printf( &logger, "Gain decreased: %.3f\r\n", gain );
            return waveform4_set_gain ( &waveform4, channel, gain );
        }
        case 'S': case 's': 
        {
            wave = WAVEFORM4_WAVE_SINE;
            log_printf( &logger, "Sine wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'C': case 'c': 
        {
            wave = WAVEFORM4_WAVE_COSINE;
            log_printf( &logger, "Cosine wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'T': case 't': 
        {
            wave = WAVEFORM4_WAVE_TRIANGLE;
            log_printf( &logger, "Triangle wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'P': case 'p': 
        {
            wave = WAVEFORM4_WAVE_POSITIVE_SAWTOOTH;
            log_printf( &logger, "Positive sawtooth wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'N': case 'n': 
        {
            wave = WAVEFORM4_WAVE_NEGATIVE_SAWTOOTH;
            log_printf( &logger, "Negative sawtooth wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '1': 
        {
            channel = WAVEFORM4_CHANNEL_1;
            log_printf( &logger, "Channel 1 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '2': 
        {
            channel = WAVEFORM4_CHANNEL_2;
            log_printf( &logger, "Channel 2 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '3': 
        {
            channel = WAVEFORM4_CHANNEL_3;
            log_printf( &logger, "Channel 3 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '4': 
        {
            channel = WAVEFORM4_CHANNEL_4;
            log_printf( &logger, "Channel 4 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'L': case 'l': 
        {
            waveform4_display_commands ( );
            return WAVEFORM4_OK;
        }
        default :
        {
            log_error( &logger, "Wrong command." );
            return WAVEFORM4_ERROR; 
        }
    }
}

// ------------------------------------------------------------------------ END
/*!
 * @file main.c
 * @brief Waveform4 Click example
 *
 * # Description
 * This example demonstrates the use of Waveform 4 click board.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes the driver and performs the click default configuration which
 * resets the registers and sets the sine wave output with default gain and 
 * default frequency for all channels. After that it displays the list of
 * supported commands on the USB UART.
 *
 * ## Application Task
 * Depending on the command character received from USB UART it changes the 
 * signal frequency, gain or wave of the selected channel.
 *
 * @author Stefan Filipovic
 *
 */

#include "board.h"
#include "log.h"
#include "waveform4.h"

static waveform4_t waveform4;
static log_t logger;

#define GAIN_STEP 0.05  // Gain step, used for increase/decrease gain commands.
#define FREQ_STEP 100   // Frequency step, used for increase/decrease frequency commands.

uint32_t freq = WAVEFORM4_DEFAULT_FREQUENCY;
float gain = WAVEFORM4_DEFAULT_GAIN;
uint8_t channel = WAVEFORM4_CHANNEL_1;
uint8_t wave = WAVEFORM4_WAVE_SINE;

/**
 * @brief Waveform 4 display commands function.
 * @details This function displays the list of supported commands on the USB UART.
 * @return None.
 * @note None.
 */
void waveform4_display_commands ( void );

/**
 * @brief Waveform 4 parse command function.
 * @details This function checks if the input command is supported and executes it.
 * @param[in] command : Command input, for more details refer to @b waveform4_display_commands function.
 * @return @li @c  0 - Success,
 *         @li @c -1 - Wrong command or command is not executed properly.
 *
 * See #err_t definition for detailed explanation.
 * @note None.
 */
err_t waveform4_parse_command ( uint8_t command );

void application_init ( void )
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    waveform4_cfg_t waveform4_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.
    waveform4_cfg_setup( &waveform4_cfg );
    WAVEFORM4_MAP_MIKROBUS( waveform4_cfg, MIKROBUS_1 );
    if ( SPI_MASTER_ERROR == waveform4_init( &waveform4, &waveform4_cfg ) )
    {
        log_error( &logger, " Communication init." );
        for ( ; ; );
    }
    
    if ( WAVEFORM4_ERROR == waveform4_default_cfg ( &waveform4 ) )
    {
        log_error( &logger, " Default configuration." );
        for ( ; ; );
    }
    
    waveform4_display_commands ( );
    log_info( &logger, " Application Task " );
}

void application_task ( void )
{
    uint8_t command = 0;
    if ( log_read ( &logger, &command, 1 ) > 0 ) 
    {
        waveform4_parse_command ( command );
    }
}

int main ( void ) 
{
    /* Do not remove this line or clock might not be set correctly. */
    #ifdef PREINIT_SUPPORTED
    preinit();
    #endif
    
    application_init( );
    
    for ( ; ; ) 
    {
        application_task( );
    }

    return 0;
}

void waveform4_display_commands ( void )
{
    log_printf( &logger, "-------------------------------------------\r\n" );
    log_info( &logger, "- UART commands list -\r\n" );
    log_printf( &logger, "'+' - Increase frequency.\r\n" );
    log_printf( &logger, "'-' - Decrease frequency.\r\n" );
    log_printf( &logger, "'G' - Increase gain.\r\n" );
    log_printf( &logger, "'g' - Decrease gain.\r\n" );
    log_printf( &logger, "'S' or 's' - Select sine wave output.\r\n" );
    log_printf( &logger, "'C' or 'c' - Select cosine wave output.\r\n" );
    log_printf( &logger, "'T' or 't' - Select triangle wave output.\r\n" );
    log_printf( &logger, "'P' or 'p' - Select positive sawtooth wave output.\r\n" );
    log_printf( &logger, "'N' or 'n' - Select negative sawtooth wave output.\r\n" );
    log_printf( &logger, "'1' - Select channel 1.\r\n" );
    log_printf( &logger, "'2' - Select channel 2.\r\n" );
    log_printf( &logger, "'3' - Select channel 3.\r\n" );
    log_printf( &logger, "'4' - Select channel 4.\r\n" );
    log_printf( &logger, "'L' or 'l' - Display commands list.\r\n" );
    log_printf( &logger, "-------------------------------------------\r\n" );
}

err_t waveform4_parse_command ( uint8_t command )
{
    switch( command )
    {
        case '+': 
        {
            freq += FREQ_STEP;
            if ( freq > WAVEFORM4_MASTER_CLOCK )
            {
                freq = WAVEFORM4_MASTER_CLOCK;
            }
            log_printf( &logger, "Frequency increased: %lu Hz\r\n", freq );
            return waveform4_set_frequency ( &waveform4, freq );
        }
        case '-': 
        {
            freq -= FREQ_STEP;
            if ( freq > WAVEFORM4_MASTER_CLOCK )
            {
                freq = 0;
            }
            log_printf( &logger, "Frequency decreased: %lu Hz\r\n", freq );
            return waveform4_set_frequency ( &waveform4, freq );
        }
        case 'G': 
        {
            gain += GAIN_STEP;
            if ( gain > WAVEFORM4_GAIN_MAX )
            {
                gain = WAVEFORM4_GAIN_MAX;
            }
            log_printf( &logger, "Gain increased: %.3f\r\n", gain );
            return waveform4_set_gain ( &waveform4, channel, gain );
        }
        case 'g': 
        {
            gain -= GAIN_STEP;
            if ( gain < WAVEFORM4_GAIN_MIN )
            {
                gain = WAVEFORM4_GAIN_MIN;
            }
            log_printf( &logger, "Gain decreased: %.3f\r\n", gain );
            return waveform4_set_gain ( &waveform4, channel, gain );
        }
        case 'S': case 's': 
        {
            wave = WAVEFORM4_WAVE_SINE;
            log_printf( &logger, "Sine wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'C': case 'c': 
        {
            wave = WAVEFORM4_WAVE_COSINE;
            log_printf( &logger, "Cosine wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'T': case 't': 
        {
            wave = WAVEFORM4_WAVE_TRIANGLE;
            log_printf( &logger, "Triangle wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'P': case 'p': 
        {
            wave = WAVEFORM4_WAVE_POSITIVE_SAWTOOTH;
            log_printf( &logger, "Positive sawtooth wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'N': case 'n': 
        {
            wave = WAVEFORM4_WAVE_NEGATIVE_SAWTOOTH;
            log_printf( &logger, "Negative sawtooth wave selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '1': 
        {
            channel = WAVEFORM4_CHANNEL_1;
            log_printf( &logger, "Channel 1 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '2': 
        {
            channel = WAVEFORM4_CHANNEL_2;
            log_printf( &logger, "Channel 2 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '3': 
        {
            channel = WAVEFORM4_CHANNEL_3;
            log_printf( &logger, "Channel 3 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case '4': 
        {
            channel = WAVEFORM4_CHANNEL_4;
            log_printf( &logger, "Channel 4 selected.\r\n" );
            return waveform4_set_wave_output ( &waveform4, channel, wave );
        }
        case 'L': case 'l': 
        {
            waveform4_display_commands ( );
            return WAVEFORM4_OK;
        }
        default :
        {
            log_error( &logger, "Wrong command." );
            return WAVEFORM4_ERROR; 
        }
    }
}

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

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