Intermediate
30 min

Bridge TTL/CMOS to RS232 using MAX3237E and STM32F413ZH

Where logic meets legacy: UART to RS232 made simple

RS232 2 Click with Nucleo 144 with STM32F413ZH MCU

Published Feb 14, 2024

Click board™

RS232 2 Click

Dev. board

Nucleo 144 with STM32F413ZH MCU

Compiler

NECTO Studio

MCU

STM32F413ZH

Unlock the full potential of serial communication with our UART-to-RS232 bridge, offering effortless signal conversion and data transfer capabilities

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Hardware Overview

How does it work?

RS232 2 Click is based on the MAX3237E, a 3V to 5.5V multichannel RS232, 1 Mbit/s line driver/receiver from Texas Instruments. This device allows communication at 1 Mbit/s and allows 5V logic levels, even when working with 3.3V power supply. However, there is an onboard SMD jumper that allows selection of power supply voltage between 3.3V and 5V, if there is a requirement. The MAX3237E IC consists of five line drivers, three line receivers, and a dual charge pump circuit with ±15 kV pin to pin ESD protection for the serial port I/O pins. Those charge pumps along with the external capacitors, allow the device to run from a single 3V to 5.5V supply, providing the required RS232

voltage levels, which can go up to ±15 V as per standard. The MAX3237E IC generates an RS232 voltage in the range of ±13 V and accepts RS232 signal levels in the range of ±25 V. To provide the minimal functionality of the UART interface, at least three data lines have to be used: RX line, routed to the mikroBUS™ RX pin (on the click board side), TX line, routed to the mikroBUS™ TX pin (on the click board side), and the GND. Otherwise, this device supports the full stack of RS232 control lines, excluding the Data Set Ready line (DSR). Other relevant RS232 bus lines routed to the mikroBUS™ pins are: Data Terminal Ready (DTR) - routed to the AN pin, Data Carrier Detect

(DCD) - routed to the RST pin, Clear To Send (CTS) - routed to the CS pin, Ring Indicator (RI) - routed to the PWM pin, Request To Send (RTS) - routed to the INT pin. All these lines, are actually control lines and are used optionally by the RS232 device. RS232 2 click features the standardized DE-9 connector for easy connection to the RS232 device. By switching the VCC SEL jumper, it is possible to select the power supply voltage for the RS232 2 click. Although it can work with 5V, the device will accept UART signals of 5V even while working in 3.3V mode.

RS232 2 Click top side image
RS232 2 Click bottom side image

Features overview

Development board

Nucleo-144 with STM32F413ZH MCU board offers an accessible and adaptable avenue for users to explore new ideas and construct prototypes. It allows users to tailor their experience by selecting from a range of performance and power consumption features offered by the STM32 microcontroller. With compatible boards, the

internal or external SMPS dramatically decreases power usage in Run mode. Including the ST Zio connector, expanding ARDUINO Uno V3 connectivity, and ST morpho headers facilitate easy expansion of the Nucleo open development platform. The integrated ST-LINK debugger/programmer enhances convenience by

eliminating the need for a separate probe. Moreover, the board is accompanied by comprehensive free software libraries and examples within the STM32Cube MCU Package, further enhancing its utility and value.

Nucleo 144 with STM32F413ZH MCU double side image

Microcontroller Overview

MCU Card / MCU

default

Architecture

ARM Cortex-M4

MCU Memory (KB)

1536

Silicon Vendor

STMicroelectronics

Pin count

144

RAM (Bytes)

327680

You complete me!

Accessories

Click Shield for Nucleo-144 comes equipped with four mikroBUS™ sockets, with one in the form of a Shuttle connector, allowing all the Click board™ devices to be interfaced with the STM32 Nucleo-144 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. Featuring an ARM Cortex-M microcontroller, 144 pins, and Arduino™ compatibility, the STM32 Nucleo-144 board offers limitless possibilities for prototyping and creating diverse applications. These boards are controlled and powered conveniently through a USB connection to program and efficiently debug the Nucleo-144 board out of the box, with an additional USB cable connected to the USB mini port on the board. Simplify your project development with the integrated ST-Link debugger and unleash creativity using the extensive I/O options and expansion capabilities. 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-144 board with our Click Shield for Nucleo-144, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.

Click Shield for Nucleo-144 accessories 1 image

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.

RS232 2 Click accessories image

Used MCU Pins

mikroBUS™ mapper

Ready to Receive
PC0
AN
Carrier Receiving Indication
PA13
RST
UART CTS
PA4
CS
NC
NC
SCK
NC
NC
MISO
NC
NC
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
UART RI
PC6
PWM
UART RTS
PF13
INT
UART TX
PA9
TX
UART RX
PA10
RX
NC
NC
SCL
NC
NC
SDA
Power Supply
5V
5V
Ground
GND
GND
1

Take a closer look

Click board™ Schematic

RS232 2 Click Schematic schematic

Step by step

Project assembly

Click Shield for Nucleo-144 accessories 1 image hardware assembly

Start by selecting your development board and Click board™. Begin with the Nucleo 144 with STM32F413ZH MCU as your development board.

Click Shield for Nucleo-144 accessories 1 image hardware assembly
Nucleo 144 with STM32F446ZE MCU front image hardware assembly
Charger 27 Click front image hardware assembly
Prog-cut hardware assembly
Charger 27 Click complete accessories setup image hardware assembly
Board mapper by product8 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
STM32F413ZH Nucleo 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 RS232 2 Click driver.

Key functions:

  • rs2322_set_cts - This function sets CTS pin state

  • rs2322_get_dtr - This function get DTR pin state

  • rs2322_send_command - Function for send command

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
}

int main ( void ) 
{
    /* Do not remove this line or clock might not be set correctly. */
    #ifdef PREINIT_SUPPORTED
    preinit();
    #endif
    
    application_init( );
    
    for ( ; ; ) 
    {
        application_task( );
    }

    return 0;
}

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

Additional Support

Resources

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