Modernize RS232 connections with MAX3232 and STM32F091RC
Upgrading data transfer: The only UART-to-RS232 bridge you need
Published Feb 26, 2024
Click board™
RS232 Click
Dev. board
Nucleo-64 with STM32F091RC MCU
Compiler
NECTO Studio
MCU
STM32F091RC
Efficient solution for incorporating RS-232 communication capabilities into various electronic projects and applications, including serial data exchange and modem communication
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Hardware Overview
How does it work?
RS232 Click is based on the MAX3232, a low-power, true RS-232 transceiver from Analog Devices. Several protection features improve the reliability of this device. It has up to ±15kV ESD protection, ensuring no electrical discharge damages the circuit on the input side. The MAX3232 has two receivers and two transmitter channels, and it is used to bridge the physical differences between the CMOS/TTL signal levels and RS-232 bus levels. While CMOS/TTL signal levels vary from 0V to 5V typically, RS-232 uses signal levels that range from ±5V up to ±15 V. Furthermore, the RS-232 equipment is required to withstand short circuits for any voltage, up to ±25V, during an indefinite time interval. MAX3232 IC uses two internal charge pumps to obtain required driving levels of ±5V on its transceiver sections.
This Click board™ offers two inputs and two outputs, which feature the CMOS/TTL logic levels. These lines can be used to either drive the RS-232 bus or receive the incoming data from the bus. Receivers convert the RS-232 signals to MCU-acceptable UART-type signals, while transmitters convert the MCU UART signal to RS-232 levels. Therefore, one input/output pair is routed to the UART pins of the mikroBUS™, allowing simplified operation by the host MCU, while another pair of input/output signals is routed via the J2 and J3 SMD jumpers and is used as the UART RTS and CTS. These pins are typically used for the UART communication with the hardware flow control. The jumpers are unpopulated by default. The MAX3232 device can maintain a 120kbps data rate with the worst-case scenario - load of 3kΩ in parallel with
1000pF, while the typical communication speed goes up to 232 kbps. The RS232 Click comes equipped with the SUB D connector, typically found on many devices that use the RS-232 interface, and can be used for connection directly to the RS-232 bus. RS232 uses a standard 2-Wire UART interface to communicate with the host MCU. If using it with soldered J2 and J3 jumpers, then you can use the UART RTS and CTS hardware flow control pins. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the PWR SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. 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.
DB9 Cable Female-to-Female (2m) cable is essential for establishing dependable serial data connections between devices. With its DB9 female connectors on both ends, this cable enables a seamless link between various equipment, such as computers, routers, switches, and other serial devices. Measuring 2 meters in length, it offers flexibility in arranging your setup without compromising data transmission quality. Crafted with precision, this cable ensures consistent and reliable data exchange, making it suitable for industrial applications, office environments, and home setups. Whether configuring networking equipment, accessing console ports, or utilizing serial peripherals, this cable's durable construction and robust connectors guarantee a stable connection. Simplify your data communication needs with the 2m DB9 female-to-female cable, an efficient solution designed to meet your serial connectivity requirements easily and efficiently.
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 RS232 Click driver.
Key functions:
rs232_generic_write- Generic write function.rs232_generic_read- Generic read function.
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
* \brief Rs232 Click example
*
* # Description
* This example reads and processes data from RS232 clicks.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes driver.
*
* ## Application Task
* Depending on the selected mode (receiver/transmitter) this function reads/sends an appropriate message.
* All data is displayed on USB UART.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "rs232.h"
#include "string.h"
#define PROCESS_RX_BUFFER_SIZE 500
#define RS232_TRANSMITTER
// #define RS232_RECEIVER
// ------------------------------------------------------------------ VARIABLES
static rs232_t rs232;
static log_t logger;
static int32_t rsp_size;
static char uart_rx_buffer[ PROCESS_RX_BUFFER_SIZE ] = { 0 };
static char message[ ] = "MikroE";
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( void )
{
log_cfg_t log_cfg;
rs232_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.
rs232_cfg_setup( &cfg );
RS232_MAP_MIKROBUS( cfg, MIKROBUS_1 );
rs232_init( &rs232, &cfg );
Delay_ms( 100 );
#ifdef RS232_RECEIVER
log_printf( &logger, " ** RS232 Receiver **\r\n" );
#endif
#ifdef RS232_TRANSMITTER
log_printf( &logger, " ** RS232 Transmitter **\r\n" );
#endif
}
void application_task ( void )
{
#ifdef RS232_RECEIVER
rsp_size = rs232_generic_read( &rs232, uart_rx_buffer, PROCESS_RX_BUFFER_SIZE );
if ( rsp_size == strlen( message ) )
{
log_printf( &logger, "Message received: %s", uart_rx_buffer );
log_printf( &logger, "\r\n-------------------------\r\n" );
memset( uart_rx_buffer, 0, rsp_size );
}
Delay_ms( 100 );
#endif
#ifdef RS232_TRANSMITTER
rs232_generic_write( &rs232, message, strlen( message ) );
log_printf( &logger, "Message sent: %s", message );
log_printf( &logger, "\r\n-------------------------\r\n" );
Delay_ms( 1000 );
#endif
}
void main ( void )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
