Intermediate
30 min
0

Ensure error-free and robust RS485 data transfer in harsh environments using MAX3471 and TM4C1294KCPDT

Simplify, optimize, transform: The future of data communication!

RS485 2 Click with UNI-DS v8

Published Oct 19, 2023

Click board™

RS485 2 Click

Development board

UNI-DS v8

Compiler

NECTO Studio

MCU

TM4C1294KCPDT

Our solution seamlessly transforms UART signals to RS485, empowering industrial automation systems with faster and more reliable data communication.

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Hardware Overview

How does it work?

RS485 2 Click is based on the MAX3471, an RS-422/485, half-duplex, differential transceiver for battery-powered systems, from Analog Devices. This click is intended to be used as a physical layer device, often referred to as PHY, providing physical interfacing of the MCU TTL level UART lines with the RS422/485 bus. It is well suited for transmitting smaller blocks of data over long distances, using a shielded differential pair, for both TX and RX signals, allowing for half-duplex asynchronous communication. The MAX3471 transceiver consists of a separate driver and receiver sections, with Driver Enable and Receiver Enable pins (#RE and DE), used to enable appropriate sections. Driver section is used to drive the RS422/485 bus with the signal received on the UART RX line labeled as RO on the IC, while the receiver section returns data from the bus back to the MCU via the UART TX line, labeled as DI on the IC in the schematics. RS422/485 standard only specifies electrical characteristics of the transmitter and the receiver. It does not specify or recommend any communications protocol, only the physical layer. The top layer communication protocol of choice can be used, such as the MODBUS or similar protocols. Therefore RS485 2 click offers UART RX and TX pins, routed to the appropriate mikroBUS™ TX and RX UART pins. These pins are used by the MCU to send data to the RS485 bus, in a form determined by the user protocol. Additional DE and RE pins are routed to the mikroBUS™ CS and PWM pin respectively. These pins are labeled on

the Click board™ as DE and RE, the same as on the IC itself. Pull-up and pull-down are used to determine states on these pins when they are left floating. MAX3471 IC allows data rates up to 64kbps. In general, the maximal transfer speed is determined by the bus length: longer bus lines will result in less transfer speed. The RS485/422 bus needs to be terminated with the resistor on both ends, which is equal to the characteristic impedance of the used cable, in order to prevent line reflections. However, the MAX3471 IC features a reduced slew rate on its driver outputs, resulting with slower speed, but with far more robust signal at the same time, which is immune to EMI and other types of interferences that appear on long lines or connection stubs (unterminated parts of the bus). This IC is also able to work on the unterminated bus, commonly used in low speed and low power systems. The RS-485 standard specifies that a compliant driver must be able to drive 32 unit loads (UL), where 1 unit load represents a load impedance of approximately 12 kΩ. Since the MAX3471 IC device is 1/8 UL, up to 256 such receivers can be supported by a single driver. In cases when the RS485/422 bus voltage is close to 2.5V, the device is able to drive up to 8 loads, which means that it can drive up to 64 receivers. As the bus voltage rises, more drivers can be added, so that for 5V the device can drive the number of devices specified by the standard. There are situations on the RS485/422 bus, which might lead to a differential voltage which can

increase the current which runs through the driver output. This state is known as the bus contention, and it commonly appears during the initialization, bus fault conditions, or with multiple nodes, which have their drivers active at the same time. The MAX3471 IC provides driver output protection, which limits this current and prevents damage to the driver output stage. The MAX3471 receiver employs input filtering and input hysteresis to enhance noise immunity when differential signals have very slow rise and fall times. MAX3471 IC features a true fail-safe receiver input, which guarantees a logic HIGH receiver output in cases when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled. There is one 4-pole screw terminal on board (VCC, RX, TX, GND) for connecting RS422/485 bus twisted pair cable, along with the GND and VCC. The jumper labeled as VCC SEL is used to set the operating voltage of the Click board™ to either 3.3V or 5V. GND and VCC rails can be used to provide the power supply for another node. Note that the VCC terminal is directly routed to either 3.3V or 5V rail of the mikroBUS™, depending on the VCC SEL jumper position. MikroElektronika provides a library that contains functions compatible with the MikroElektronika compilers, which can be used for working with the RS485 2 Click. The library also contains an example application, which demonstrates their use. This example application can be used as a reference for custom designs.

RS485 2 Click top side image
RS485 2 Click bottom side image

Features overview

Development board

UNI-DS v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different STM32, Kinetis, TIVA, CEC, MSP, PIC, dsPIC, PIC32, and AVR MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. 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, UNI-DS v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the UNI-DS v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it 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

HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. UNI-DS 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.

UNI-DS v8 horizontal image

Microcontroller Overview

MCU Card / MCU

default

Type

8th Generation

Architecture

ARM Cortex-M4

MCU Memory (KB)

512

Silicon Vendor

Texas Instruments

Pin count

128

RAM (Bytes)

262144

Used MCU Pins

mikroBUS™ mapper

NC
NC
AN
NC
NC
RST
Driver Output Enable
PH0
CS
NC
NC
SCK
NC
NC
MISO
NC
NC
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
Receiver Output Enable
PL4
PWM
NC
NC
INT
UART TX
PK1
TX
UART RX
PK0
RX
NC
NC
SCL
NC
NC
SDA
Power Supply
5V
5V
Ground
GND
GND
1

Take a closer look

Schematic

RS485 2 Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI-DS v8 as your development board.

Fusion for PIC v8 front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
v8 SiBRAIN 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 Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for RS485 2 Click driver.

Key functions:

  • rs4852_generic_read - Generic read function.

  • rs4852_generic_write - Generic write function.

  • rs4852_set_de_pin - Set DE ( cs ) pin state.

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 Rs4852 Click example
 * 
 * # Description
 * This example reads and processes data from RS485 2 clicks.
 *
 * The demo application is composed of two sections :
 * 
 * ## Application Init 
 * Initializes the driver and enables the selected mode.
 * 
 * ## Application Task  
 * Depending on the selected mode, it reads all the received data or sends the desired message
 * every 2 seconds.
 * 
 * ## Additional Function
 * - rs4852_process ( ) - The general process of collecting the received data.
 * 
 * \author MikroE Team
 *
 */
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "rs4852.h"
#include "string.h"

#define PROCESS_RX_BUFFER_SIZE 500

#define TEXT_TO_SEND "MikroE - RS485 2 click board\r\n"

// #define DEMO_APP_RECEIVER
#define DEMO_APP_TRANSMITTER

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

static rs4852_t rs4852;
static log_t logger;

// ------------------------------------------------------- ADDITIONAL FUNCTIONS

static void rs4852_process ( void )
{
    int32_t rsp_size;
    
    char uart_rx_buffer[ PROCESS_RX_BUFFER_SIZE ] = { 0 };
    uint8_t check_buf_cnt;
    
    rsp_size = rs4852_generic_read( &rs4852, uart_rx_buffer, PROCESS_RX_BUFFER_SIZE );

    if ( rsp_size > 0 )
    {  
        for ( uint8_t cnt = 0; cnt < rsp_size; cnt++ )
        {
            log_printf( &logger, "%c", uart_rx_buffer[ cnt ] );
            if ( uart_rx_buffer[ cnt ] == '\n' )
            {
                log_printf( &logger, "--------------------------------\r\n" );
            }
        }
    }
}

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

void application_init ( void )
{
    log_cfg_t log_cfg;
    rs4852_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.

    rs4852_cfg_setup( &cfg );
    RS4852_MAP_MIKROBUS( cfg, MIKROBUS_1 );
    rs4852_init( &rs4852, &cfg );
    Delay_ms( 100 );
    
#ifdef DEMO_APP_RECEIVER
    rs4852_set_re_pin( &rs4852, RS4852_ENABLE_RE );
    rs4852_set_de_pin( &rs4852, RS4852_DISABLE_DE );
    log_info( &logger, "---- Receiver mode ----" );
#endif    
#ifdef DEMO_APP_TRANSMITTER
    rs4852_set_de_pin( &rs4852, RS4852_ENABLE_DE );
    rs4852_set_re_pin( &rs4852, RS4852_DISABLE_RE );
    log_info( &logger, "---- Transmitter mode ----" );
#endif    
    Delay_ms( 100 );
}

void application_task ( void )
{
#ifdef DEMO_APP_RECEIVER
    rs4852_process( );
#endif    
    
#ifdef DEMO_APP_TRANSMITTER
    rs4852_generic_write( &rs4852, TEXT_TO_SEND, strlen( TEXT_TO_SEND ) );
    log_info( &logger, "---- Data sent ----" );
    Delay_ms( 2000 );
#endif   
}

void main ( void )
{
    application_init( );

    for ( ; ; )
    {
        application_task( );
    }
}

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

Additional Support

Resources