Intermediate
20 min

Achieve communication with external devices over telephone lines or data networks with CMX869B and ATmega328P

Low-power modem solution for EPOS (Electronic Point of Sale) terminals and telephone-based systems

EPOS Module Click with Arduino UNO Rev3

Published Sep 23, 2024

Click board™

EPOS Module Click

Dev Board

Arduino UNO Rev3

Compiler

NECTO Studio

MCU

ATmega328P

Enable secure, low-power modem communication for EPOS terminals and remote systems ideal for reliable data transfer in industrial control and security applications

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Hardware Overview

How does it work?

EPOS Module Click is based on the CMX869B, a multi-standard v.32 bis modem from CML Micro, which supports multiple protocols while offering low power consumption. This low-power modem solution is designed for applications involving EPOS (Electronic Point of Sale) terminals and telephone-based systems. The CMX869B supports standards such as ITU V.32 bis, V.22 bis, V.22, V.21, and Bell 202 and 103, making it adaptable for numerous communication scenarios. It operates at data rates of up to 14.400bps and features automatic fallback to 4.800bps, with capabilities like retrain rate re-negotiation and automatic detection of V.22 and V.22 bis modems. This Click board™ is ideal for use in EPOS terminals, telephone telemetry systems, remote utility meter reading, security systems, industrial control, and other applications. In addition to its robust modem

functions, the CMX869B includes a high-quality DTMF (Dual-Tone Multi-Frequency) encoder and decoder, making it suitable for managing call signaling and detection in telephone systems. The modem can also transmit and detect user-programmed single and dual-tone signals, as well as handle modem calling and answering tones, ensuring compatibility with various proprietary communication protocols beyond standard modem operations. The Click board™ also offers a fully isolated EPOS/telephone-based connection, thanks to its built-in P1200 transformer, which ensures smooth communication while providing complete electrical isolation. Data and control exchanges between the CMX869B and the host MCU are made through a C-BUS interface, compatible with a standard 4-wire SPI interface of the mikroBUS™ socket. The board also uses the mikroBUS™

socket's IRQ pin for interrupt requests related to call states like busy, dialing, and connected statuses, a red RING LED to indicate ringing signals, and a blue HOOK LED that serves as a hookswitch indicator to manage the line interface's connectivity status (0-OFF, 1-ON). An additional feature of the CMX869B is the Powersave mode, which conserves energy by deactivating all circuits except the essential C-BUS (SPI) interface. This Click board™ can be operated only with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. Also, it comes equipped with a library containing functions and an example code that can be used as a reference for further development.

EPOS Module Click hardware overview image

Features overview

Development board

Arduino UNO is a versatile microcontroller board built around the ATmega328P chip. It offers extensive connectivity options for various projects, featuring 14 digital input/output pins, six of which are PWM-capable, along with six analog inputs. Its core components include a 16MHz ceramic resonator, a USB connection, a power jack, an

ICSP header, and a reset button, providing everything necessary to power and program the board. The Uno is ready to go, whether connected to a computer via USB or powered by an AC-to-DC adapter or battery. As the first USB Arduino board, it serves as the benchmark for the Arduino platform, with "Uno" symbolizing its status as the

first in a series. This name choice, meaning "one" in Italian, commemorates the launch of Arduino Software (IDE) 1.0. Initially introduced alongside version 1.0 of the Arduino Software (IDE), the Uno has since become the foundational model for subsequent Arduino releases, embodying the platform's evolution.

Arduino UNO Rev3 double side image

Microcontroller Overview

MCU Card / MCU

default

Architecture

AVR

MCU Memory (KB)

32

Silicon Vendor

Microchip

Pin count

28

RAM (Bytes)

2048

You complete me!

Accessories

Click Shield for Arduino UNO has two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the Arduino UNO board without effort. The Arduino Uno, a microcontroller board based on the ATmega328P, provides an affordable and flexible way for users to try out new concepts and build prototypes with the ATmega328P microcontroller from various combinations of performance, power consumption, and features. The Arduino Uno has 14 digital input/output pins (of which six can be used as PWM outputs), six analog inputs, a 16 MHz ceramic resonator (CSTCE16M0V53-R0), a USB connection, a power jack, an ICSP header, and reset button. Most of the ATmega328P 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 Arduino UNO board with our Click Shield for Arduino UNO, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.

Click Shield for Arduino UNO accessories 1 image

Used MCU Pins

mikroBUS™ mapper

NC
NC
AN
NC
NC
RST
SPI Chip Select
PB2
CS
SPI Clock
PB5
SCK
SPI Data OUT
PB4
MISO
SPI Data IN
PB3
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
NC
NC
PWM
Interrupt Request
PC3
INT
NC
NC
TX
NC
NC
RX
NC
NC
SCL
NC
NC
SDA
NC
NC
5V
Ground
GND
GND
1

Take a closer look

Schematic

EPOS Module Click Schematic schematic

Step by step

Project assembly

Click Shield for Arduino UNO front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Arduino UNO Rev3 as your development board.

Click Shield for Arduino UNO front image hardware assembly
Arduino UNO Rev3 front image hardware assembly
Charger 27 Click front image hardware assembly
Prog-cut hardware assembly
Charger 27 Click complete accessories setup image hardware assembly
Arduino UNO Rev3 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
Arduino UNO 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 EPOS Module Click driver.

Key functions:

  • eposmodule_handshake_init - This function performs a handshake init which resets the device settings to default.

  • eposmodule_dial - This function dials the selected number by alternating between DTMF and No-tone.

  • eposmodule_send_message - This function sends an array of bytes via V.23 FSK 1200bps modem in start-stop 8.1 mode.

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 EPOS Module Click example
 *
 * # Description
 * This example demonstrates the use of EPOS Module click board by showing
 * the communication between the two click boards connected to PBX system.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes the driver and logger, and displays the selected application mode.
 *
 * ## Application Task
 * Dialing application mode:
 * - Resets the device settings and dials the selected number. If a call is answered
 * it starts sending desired messages every couple of seconds with constantly checking
 * if a call is still in progress or it's terminated from the other side.
 * Answering application mode:
 * - Resets the device settings and waits for an incoming call indication, answers the call,
 * and waits for a desired number of messages. The call is terminated after all messages
 * are received successfully.
 *
 * @note
 * We have used a Yeastar S20 VoIP PBX system for the test, where the click boards are
 * connected to ports 1 and 2 configured as FXS extension with numbers 1000 and 1001 (dialer).
 *
 * @author Stefan Filipovic
 *
 */

#include "board.h"
#include "log.h"
#include "eposmodule.h"

// Demo aplication selection macros
#define APP_DIALING                 0
#define APP_ANSWERING               1
#define DEMO_APP                    APP_DIALING

// Dialing application settings - a dial number and text to send (must end with CRLF - \r\n)
#define DIAL_NUMBER                 "1000"
#define TEXT_TO_SEND                "MIKROE - EPOS Module click\r\n"

// Answering application settings - a number of successfully received messages before call termination
#define NUM_MESSAGES                5u

static eposmodule_t eposmodule;
static log_t logger;

void application_init ( void )
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    eposmodule_cfg_t eposmodule_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.
    eposmodule_cfg_setup( &eposmodule_cfg );
    EPOSMODULE_MAP_MIKROBUS( eposmodule_cfg, MIKROBUS_1 );
    if ( SPI_MASTER_ERROR == eposmodule_init( &eposmodule, &eposmodule_cfg ) )
    {
        log_error( &logger, " Communication init." );
        for ( ; ; );
    }

#if ( DEMO_APP == APP_DIALING )
    log_printf( &logger, " Application Mode: Dialing\r\n" );
#elif ( DEMO_APP == APP_ANSWERING )
    log_printf( &logger, " Application Mode: Answering\r\n" );
#else
    #error "Selected application mode is not supported!"
#endif
    
    log_info( &logger, " Application Task " );
}

void application_task ( void )
{
    uint8_t state = EPOSMODULE_STATE_IDLE;
    uint32_t time_cnt = 0;
    uint8_t msg_cnt = 0;

    eposmodule_handshake_init ( &eposmodule );

#if ( DEMO_APP == APP_DIALING )
    log_printf( &logger, "\r\n Hook OFF\r\n" );
    eposmodule_hook_off ( &eposmodule );
    Delay_ms ( 4000 );
    log_printf( &logger, " Dial: %s\r\n", ( char * ) DIAL_NUMBER );
    eposmodule_dial ( &eposmodule, DIAL_NUMBER );
    eposmodule.rx_mode &= EPOSMODULE_RX_LEVEL_MASK; // No change in rx level setting
    eposmodule.rx_mode |= ( EPOSMODULE_RX_MODE_DTMF_TONES | EPOSMODULE_RX_TONE_DETECT_CALL_PROG );
    eposmodule_set_receive_mode ( &eposmodule, eposmodule.rx_mode );
    for ( ; ; )
    {
        Delay_ms ( 1 );
        if ( !eposmodule_get_irq_pin ( &eposmodule ) )
        {
            time_cnt = 0;
            state = EPOSMODULE_STATE_IRQ_SET;
        }
        if ( ( EPOSMODULE_STATE_IRQ_SET == state ) && !eposmodule_call_progress ( &eposmodule ) )
        {
            if ( time_cnt < EPOSMODULE_TIMING_BUSY )
            {
                log_printf( &logger, " Busy\r\n" );
                break;
            }
            else if ( time_cnt < EPOSMODULE_TIMING_DISCONNECTED )
            {
                log_printf( &logger, " Disconnected\r\n" );
                break;
            }
            else if ( time_cnt < EPOSMODULE_TIMING_RINGING )
            {
                log_printf( &logger, " Ringing\r\n" );
                state = EPOSMODULE_STATE_RINGING;
            }
        }
        if ( ( EPOSMODULE_STATE_RINGING == state ) && ( time_cnt > EPOSMODULE_TIMING_CALL_PROGRESS ) )
        {
            log_printf( &logger, " Call in progress\r\n" );
            state = EPOSMODULE_STATE_CALL_IN_PROGRESS;
            time_cnt = 0;
        }
        if ( ( EPOSMODULE_STATE_CALL_IN_PROGRESS == state ) && !( time_cnt % EPOSMODULE_TIMING_SEND_MESSAGE ) )
        {
            log_printf( &logger, " Send message %u\r\n", ( uint16_t ) msg_cnt++ );
            eposmodule_send_message ( &eposmodule, TEXT_TO_SEND, strlen ( TEXT_TO_SEND ) );
        }
        if ( time_cnt++ > EPOSMODULE_TIMEOUT_CALL_PROGRESS )
        {
            log_printf( &logger, " Timeout\r\n" );
            break;
        }
    }
    log_printf( &logger, " Hook ON\r\n" );
    eposmodule_hook_on ( &eposmodule );
    Delay_ms ( 4000 );
#elif ( DEMO_APP == APP_ANSWERING )
    uint8_t rx_data = 0;
    uint8_t msg_end_buff[ 2 ] = { 0 };

    log_printf( &logger, "\r\n Waiting for a call...\r\n" );

    while ( !eposmodule_ring_detect ( &eposmodule ) );

    Delay_ms ( 1000 );
    log_printf( &logger, " Hook OFF\r\n" );
    eposmodule_hook_off ( &eposmodule );
    Delay_ms ( 1000 );
    log_printf( &logger, " Waiting for %u messages...\r\n", ( uint16_t ) NUM_MESSAGES );
    eposmodule.rx_mode &= EPOSMODULE_RX_LEVEL_MASK; // No change in rx level setting
    eposmodule.rx_mode |= ( EPOSMODULE_RX_MODE_V23_FSK_1200 | EPOSMODULE_RX_DATA_FORMAT_SS_NO_OVS | 
                            EPOSMODULE_RX_DATA_PARITY_8_NO_PAR );
    eposmodule_set_receive_mode ( &eposmodule, eposmodule.rx_mode );

    for ( ; ; )
    {
        Delay_ms ( 1 );
        if ( !eposmodule_get_irq_pin ( &eposmodule ) )
        {
            if ( EPOSMODULE_STATE_IDLE != state )
            {
                log_printf( &logger, "\r\n Disconnected\r\n" );
                break;
            }
            log_printf( &logger, " Message %u: ", ( uint16_t ) msg_cnt );
            state = EPOSMODULE_STATE_IRQ_SET;
            time_cnt = 0;
        }
        if ( ( EPOSMODULE_STATE_IRQ_SET == state ) && !( time_cnt % EPOSMODULE_TIMING_RX_READY ) )
        {
            if ( eposmodule_unscram_1s_det ( &eposmodule ) && eposmodule_rx_ready ( &eposmodule ) )
            {
                eposmodule_receive_data ( &eposmodule, &rx_data );
                if ( ( ( ' ' <= rx_data ) && ( '~' >= rx_data ) ) || 
                     ( '\r' == rx_data ) || ( '\n' == rx_data ) )
                {
                    log_printf( &logger, "%c", ( char ) rx_data );
                }
                if ( '\r' == rx_data )
                {
                    msg_end_buff[ 0 ] = rx_data;
                }
                else if ( '\n' == rx_data )
                {
                    msg_end_buff[ 1 ] = rx_data;
                }
                else
                {
                    msg_end_buff[ 0 ] = 0;
                    msg_end_buff[ 1 ] = 0;
                }
            }
            if ( ( '\r' == msg_end_buff[ 0 ] ) && ( '\n' == msg_end_buff[ 1 ] ) )
            {
                msg_end_buff[ 0 ] = 0;
                msg_end_buff[ 1 ] = 0;
                state = EPOSMODULE_STATE_IDLE;
                if ( NUM_MESSAGES == ++msg_cnt )
                {
                    Delay_ms ( 100 );
                    log_printf( &logger, " Terminate call\r\n" );
                    Delay_ms ( 100 );
                    break;
                }
            }
        }
        if ( time_cnt++ > EPOSMODULE_TIMING_WAIT_FOR_MESSAGE )
        {
            log_printf( &logger, "\r\n Timeout\r\n" );
            break;
        }
    }
    log_printf( &logger, " Hook ON\r\n" );
    eposmodule_hook_on ( &eposmodule );
    Delay_ms ( 4000 );
#endif
}

int main ( void ) 
{
    application_init( );
    
    for ( ; ; ) 
    {
        application_task( );
    }

    return 0;
}

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

Additional Support

Resources

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