Beginner
10 min

Connect and control remote equipment with ease using ADM485 and PIC18F57Q43

From legacy to legendary: RS485-UART conversion

RS485 Click 5V with Curiosity Nano with PIC18F57Q43

Published Feb 13, 2024

Click board™

RS485 Click 5V

Dev. board

Curiosity Nano with PIC18F57Q43

Compiler

NECTO Studio

MCU

PIC18F57Q43

Perfectly tailored to meet your low-power RS485 data communication needs, ensuring compatibility and reliability across various applications

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A

Hardware Overview

How does it work?

RS485 Click 5V is based on the ADM485, a low-power EIA RS-485 transceiver from Analog Devices. It is a tristate differential line driver and differential input line receiver intended to be used as a physical layer device, often called PHY, providing physical interfacing of the MCU TTL level UART lines with the RS422/485 bus. It is well suited for transmitting smaller data blocks over long distances, using a twisted differential signal pair for both TX and RX signals, allowing for half-duplex asynchronous communication. The ADM485 transceiver consists of separate driver and receiver sections, with Driver Enable and Receiver Enable pins used to enable the appropriate sections. The driver section drives the RS422/485 bus with the signal received on the UART RX line, while the receiver section returns data from the bus to the MCU via the UART TX line. RS422/485 standard only specifies the 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, such as the MODBUS or similar protocols, can be used. Therefore, RS485 click 5V offers UART RX and TX pins routed to the

appropriate mikroBUS™ TX and RX UART pins. The MCU uses these pins to send data to the RS485 bus in a form determined by the user protocol. The ADM485 IC allows communication with data rates up to 5 Mbps. However, the bus length determines the maximal transfer speed: longer bus lines will result in less transfer speed. The RS422/RS485 bus needs to be terminated with the resistor on both ends (so-called parallel termination), which is equal to the characteristic impedance of the used cable, to prevent line reflections. The RS485 standard prescribes using a twisted pair cable as the data bus. Twisted pair cable tends to cancel common-mode noise and cause cancellation of the magnetic fields generated by the current flowing through each wire, thereby reducing the effective inductance of the pair. The Click board™ is equipped with a jumper that can be used to route the termination resistor of 120Ω between the bus lines. It is also equipped with two more jumpers, labeled as BIAS ENABLE. These jumpers enable bus biasing by using pull-up and pull-down resistors between the bus differential lines and VCC/GND, respectively, preventing certain faulty conditions when nodrivers are

enabled on the bus, in addition to existing IC protection. RS485 Click 5V uses a standard 2-Wire UART interface to communicate with the host MCU with commonly used UART RX and TX lines. Receiver output enable (RE) and driver output enable (DE) pins of the ADM485 are joined together and routed to the R/T pin of the mikroBUS™ socket. When left floating, a pull-down resistor determines the states on these pins, so you have to enable the device by writing a High logic state. Note that DE and RE pins use opposite signal polarities for the active state, making it possible to drive them with a single MCU pin. When a HIGH logic level is applied to the R/T pin, the transmitter becomes activated, while the receiver is deactivated at the same time - and vice versa. The R/T pin acts as a communication direction pin in this configuration. This Click board™ can be operated only with a 5V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. Also, this 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.

RS485 Click 5V hardware overview image

Features overview

Development board

PIC18F57Q43 Curiosity Nano evaluation kit is a cutting-edge hardware platform designed to evaluate microcontrollers within the PIC18-Q43 family. Central to its design is the inclusion of the powerful PIC18F57Q43 microcontroller (MCU), offering advanced functionalities and robust performance. Key features of this evaluation kit include a yellow user LED and a responsive

mechanical user switch, providing seamless interaction and testing. The provision for a 32.768kHz crystal footprint ensures precision timing capabilities. With an onboard debugger boasting a green power and status LED, programming and debugging become intuitive and efficient. Further enhancing its utility is the Virtual serial port (CDC) and a debug GPIO channel (DGI

GPIO), offering extensive connectivity options. Powered via USB, this kit boasts an adjustable target voltage feature facilitated by the MIC5353 LDO regulator, ensuring stable operation with an output voltage ranging from 1.8V to 5.1V, with a maximum output current of 500mA, subject to ambient temperature and voltage constraints.

PIC18F57Q43 Curiosity Nano double side image

Microcontroller Overview

MCU Card / MCU

default

Architecture

PIC

MCU Memory (KB)

128

Silicon Vendor

Microchip

Pin count

48

RAM (Bytes)

8196

You complete me!

Accessories

Curiosity Nano Base for Click boards is a versatile hardware extension platform created to streamline the integration between Curiosity Nano kits and extension boards, tailored explicitly for the mikroBUS™-standardized Click boards and Xplained Pro extension boards. This innovative base board (shield) offers seamless connectivity and expansion possibilities, simplifying experimentation and development. Key features include USB power compatibility from the Curiosity Nano kit, alongside an alternative external power input option for enhanced flexibility. The onboard Li-Ion/LiPo charger and management circuit ensure smooth operation for battery-powered applications, simplifying usage and management. Moreover, the base incorporates a fixed 3.3V PSU dedicated to target and mikroBUS™ power rails, alongside a fixed 5.0V boost converter catering to 5V power rails of mikroBUS™ sockets, providing stable power delivery for various connected devices.

Curiosity Nano Base for Click boards accessories 1 image

Used MCU Pins

mikroBUS™ mapper

NC
NC
AN
NC
NC
RST
NC
NC
CS
NC
NC
SCK
NC
NC
MISO
NC
NC
MOSI
NC
NC
3.3V
Ground
GND
GND
Receive/Transmit
PB0
PWM
NC
NC
INT
UART TX
PC3
TX
UART RX
PC2
RX
NC
NC
SCL
NC
NC
SDA
Power Supply
5V
5V
Ground
GND
GND
1

Take a closer look

Click board™ Schematic

RS485 Click 5V Schematic schematic

Step by step

Project assembly

Curiosity Nano Base for Click boards front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Curiosity Nano with PIC18F57Q43 as your development board.

Curiosity Nano Base for Click boards front image hardware assembly
Charger 27 Click front image hardware assembly
PIC18F47Q10 Curiosity Nano front image hardware assembly
Prog-cut hardware assembly
Charger 27 Click complete accessories setup image hardware assembly
Curiosity Nano with PICXXX 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
PIC18F57Q43 Curiosity 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

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 RS485 Click 5V driver.

Key functions:

  • rs4855v_generic_read - This function reads a desired number of data bytes by using UART serial interface.

  • rs4855v_send_command - This function sends a command by using UART serial interface.

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 RS485 5V Click Example.
 *
 * # Description
 * This example reads and processes data from RS485 5V clicks.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes driver and wake-up module.
 *
 * ## Application Task
 * Reads the received data and parses it.
 *
 * ## Additional Function
 * - static void rs4855v_clear_current_rsp_buf ( void ) - The general process of clearing buffer.
 * - static void rs4855v_process ( void ) - The general process of collecting the received data.
 * @author Stefan Ilic
 *
 */
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "rs4855v.h"
#include "string.h"

#define PROCESS_COUNTER 10
#define PROCESS_RX_BUFFER_SIZE 100
#define PROCESS_PARSER_BUFFER_SIZE 100

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

//#define DEMO_APP_RECEIVER
#define DEMO_APP_TRANSMITTER

static rs4855v_t rs4855v;
static log_t logger;

static char current_rsp_buf[ PROCESS_PARSER_BUFFER_SIZE ];
static uint8_t send_data_cnt = 0; 

unsigned char demo_message[ 9 ] = { 'M', 'i', 'k', 'r', 'o', 'E', 13, 10, 0 };
// ------------------------------------------------------- ADDITIONAL FUNCTIONS

static void rs4855v_clear_current_rsp_buf ( void ) {
    memset( current_rsp_buf, 0, PROCESS_PARSER_BUFFER_SIZE );
}

static void rs4855v_process ( void ) {
    int16_t rsp_size;
    uint16_t rsp_cnt = 0;

    char uart_rx_buffer[ PROCESS_RX_BUFFER_SIZE ] = { 0 };
    uint8_t check_buf_cnt;
    uint8_t process_cnt = PROCESS_COUNTER;

    // Clear parser buffer
    memset( current_rsp_buf, 0 , PROCESS_PARSER_BUFFER_SIZE ); 

    while( process_cnt != 0 ) {
        rsp_size = rs4855v_generic_read( &rs4855v, &uart_rx_buffer, PROCESS_RX_BUFFER_SIZE );

        if ( rsp_size > 0 ) {  
            // Validation of the received data
            for ( check_buf_cnt = 0; check_buf_cnt < rsp_size; check_buf_cnt++ ) {
                if ( uart_rx_buffer[ check_buf_cnt ] == 0 ) {
                    uart_rx_buffer[ check_buf_cnt ] = 13;
                }
            }
            // Storages data in parser buffer
            rsp_cnt += rsp_size;
            if ( rsp_cnt < PROCESS_PARSER_BUFFER_SIZE ) {
                strncat( current_rsp_buf, uart_rx_buffer, rsp_size );
            }
            
            // Clear RX buffer
            memset( uart_rx_buffer, 0, PROCESS_RX_BUFFER_SIZE );
        } 
        else {
            process_cnt--;
            
            // Process delay 
            Delay_ms( 100 );
        }
    }
}

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

void application_init ( void ) {
    log_cfg_t log_cfg;
    rs4855v_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 );

    //  Click initialization.

    rs4855v_cfg_setup( &cfg );
    RS4855V_MAP_MIKROBUS( cfg, MIKROBUS_1 );
    rs4855v_init( &rs4855v, &cfg );
    log_info( &logger, " Application Task " );
    Delay_ms( 100 );
    
#ifdef DEMO_APP_TRANSMITTER
    log_printf( &logger, "------------------\r\n" );
    log_printf( &logger, "    Send data:    \r\n" );
    log_printf( &logger, "      MikroE      \r\n" );
    log_printf( &logger, "------------------\r\n" );
    log_printf( &logger, "  Transmit data   \r\n" );
    Delay_ms( 1000 );

#endif
    
#ifdef DEMO_APP_RECEIVER 
    log_printf( &logger, "------------------\r\n" );

    log_printf( &logger, "   Receive data  \r\n" );
    Delay_ms( 2000 );
#endif
        
    log_printf( &logger, "------------------\r\n" );
}

void application_task ( void ) {  
#ifdef DEMO_APP_RECEIVER 
    
    rs4855v_process( );
    if ( current_rsp_buf > 0 ) {
        log_printf( &logger, "%s", current_rsp_buf );
        rs4855v_clear_current_rsp_buf( );
    }
    
#endif 

#ifdef DEMO_APP_TRANSMITTER
      
    rs4855v_send_command( &rs4855v, &demo_message[ 0 ] );
    log_printf( &logger, "\t%s",  &demo_message[ 0 ] );
    Delay_ms( 2000 );
    log_printf( &logger, "------------------\r\n" ); 
    
#endif   
}

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

    return 0;
}

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

Additional Support

Resources

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