Connect and control remote equipment with ease using ADM485 and STM32F091RC
From legacy to legendary: RS485-UART conversion
Published Feb 26, 2024
Click board™
RS485 Click 5V
Dev. board
Nucleo-64 with STM32F091RC MCU
Compiler
NECTO Studio
MCU
STM32F091RC
Perfectly tailored to meet your low-power RS485 data communication needs, ensuring compatibility and reliability across various applications
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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.
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.
Microcontroller Overview
MCU Card / MCU
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.
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 Nucleo-64 with STM32F091RC MCU 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 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
