Optimize your UART interface and simplify serial data communication by implementing our CMOS analog multiplexer, allowing four remote RS-232 transceivers to efficiently share a single UART connection
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Hardware Overview
How does it work?
UART MUX 2 Click is based on the MAX399, a precise CMOS analog multiplexer that enables pseudo-multidrop RS232 transmission from Analog Devices. This multiplexer allows multiple channels, in this case, four, to share a single UART interface. It offers fast switching speeds with a transition time of less than 250ns and low on-resistance of less than 100Ω while retaining CMOS-logic input compatibility and fast switching. The dual four-to-one multiplexer permits transceiver MAX3221 to form a network with the four remote transceivers connected to terminals labeled as UART0-UART3 in the upper part of the Click board™. The circuit's supply-voltage range (3V to 5.5V) makes it compatible with 3V and 5V logic. MAX399 receives its power directly from the power terminals of MAX3221, whose ±5.5V outputs come
from an internal charge pump. The multiplexer handles rail-to-rail signals, so obtaining its power from MAX3221 ensures that RS232 signals pass directly through, regardless of amplitude. The UART MUX Click communicates with MCU through MAX3221 using the UART interface for the data transfer. The MAX3221 can run at data rates up to 250 kbps while maintaining RS232-compliant output levels. Channel selection is performed through a set of specific GPIO pins, labeled as A0 and A1, routed on the CS and RST pins of the mikroBUS™ socket. Selecting channel 1, for instance, enables MAX3221 to communicate with UART0 without being loaded by UART1 to UART3. Pulldown resistors inside the remote transceivers force the outputs of un-selected receivers to a known state. In addition to a
channel selection, this Click board™ also has an automatic power-down feature that can be turned off when ON and OFF pins are high, routed on the PWM and AN pins of the mikroBUS™ socket. Also, it uses the interrupt pin of the mikroBUS™ labeled as INV as an invalid indicator, making interfacing with the RS232 simple and easy, indicating whether a valid RS232 signal is present. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC 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.
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Click board™ Schematic

Step by step
Project 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 UART MUX 2 Click driver.
Key functions:
uartmux2_set_operation_mode
- UART MUX 2 set operation mode functionuartmux2_set_channel
- UART MUX 2 set channel functionuartmux2_send_data
- UART MUX 2 data writing 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 main.c
* @brief UART MUX 2 Click Example.
*
* # Description
* This library contains API for UART MUX 2 Click driver.
* This example transmits/receives and processes data from UART MUX 2 clicks.
* The library initializes and defines the UART bus drivers
* to transmit or receive data.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes driver and set UART channel module.
*
* ## Application Task
* Transmitter/Receiver task depend on uncommented code.
* Receiver logging each received byte to the UART for data logging,
* while transmitted send messages every 2 seconds.
*
* ## Additional Function
* - static void uartmux2_clear_app_buf ( void ) - Function clears memory of app_buf.
* - static err_t uartmux2_process ( void ) - The general process of collecting presponce
* that a module sends.
*
* @author Nenad Filipovic
*
*/
#include "board.h"
#include "log.h"
#include "uartmux2.h"
#define PROCESS_BUFFER_SIZE 200
#define TRANSMITTER
// #define RECIEVER
static uartmux2_t uartmux2;
static log_t logger;
static uint8_t uart_ch;
static char app_buf[ PROCESS_BUFFER_SIZE ] = { 0 };
static int32_t app_buf_len = 0;
static int32_t app_buf_cnt = 0;
unsigned char demo_message[ 9 ] = { 'M', 'i', 'k', 'r', 'o', 'E', 13, 10, 0 };
/**
* @brief UART MUX 2 clearing application buffer.
* @details This function clears memory of application buffer and reset it's length and counter.
* @note None.
*/
static void uartmux2_clear_app_buf ( void );
/**
* @brief UART MUX 2 data reading function.
* @details This function reads data from device and concats data to application buffer.
*
* @return @li @c 0 - Read some data.
* @li @c -1 - Nothing is read.
* @li @c -2 - Application buffer overflow.
*
* See #err_t definition for detailed explanation.
* @note None.
*/
static err_t uartmux2_process ( void );
void application_init ( void ) {
log_cfg_t log_cfg; /**< Logger config object. */
uartmux2_cfg_t uartmux2_cfg; /**< Click config object. */
/**
* 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_printf( &logger, "\r\n Application Init \r\n" );
// Click initialization.
uartmux2_cfg_setup( &uartmux2_cfg );
UARTMUX2_MAP_MIKROBUS( uartmux2_cfg, MIKROBUS_1 );
err_t init_flag = uartmux2_init( &uartmux2, &uartmux2_cfg );
if ( init_flag == UART_ERROR ) {
log_error( &logger, " Application Init Error. " );
log_info( &logger, " Please, run program again... " );
for ( ; ; );
}
uartmux2_default_cfg ( &uartmux2 );
app_buf_len = 0;
app_buf_cnt = 0;
log_printf( &logger, "\r\n Application Task \r\n" );
log_printf( &logger, "------------------\r\n" );
Delay_ms( 500 );
#ifdef TRANSMITTER
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 RECIEVER
uart_ch = UARTMUX2_CHANNEL_0;
log_printf( &logger, " Receive data \r\n" );
log_printf( &logger, " UART%u \r\n", ( uint16_t ) uart_ch );
uartmux2_set_channel( &uartmux2, uart_ch );
Delay_ms( 2000 );
#endif
log_printf( &logger, "------------------\r\n" );
}
void application_task ( void ) {
#ifdef TRANSMITTER
for ( uart_ch = UARTMUX2_CHANNEL_0; uart_ch <= UARTMUX2_CHANNEL_3; uart_ch++ ) {
uartmux2_set_channel( &uartmux2, uart_ch );
Delay_ms( 100 );
uartmux2_send_data( &uartmux2, demo_message );
log_printf( &logger, " UART%u : ", ( uint16_t ) uart_ch );
for ( uint8_t cnt = 0; cnt < 9; cnt ++ ) {
log_printf( &logger, "%c", demo_message[ cnt ] );
Delay_ms( 100 );
}
}
log_printf( &logger, "------------------\r\n" );
Delay_ms( 100 );
#endif
#ifdef RECIEVER
uartmux2_process( );
if ( app_buf_len > 0 ) {
log_printf( &logger, "%s", app_buf );
uartmux2_clear_app_buf( );
}
#endif
}
void main ( void ) {
application_init( );
for ( ; ; ) {
application_task( );
}
}
static void uartmux2_clear_app_buf ( void ) {
memset( app_buf, 0, app_buf_len );
app_buf_len = 0;
app_buf_cnt = 0;
}
static err_t uartmux2_process ( void ) {
int32_t rx_size;
char rx_buff[ PROCESS_BUFFER_SIZE ] = { 0 };
rx_size = uartmux2_generic_read( &uartmux2, rx_buff, PROCESS_BUFFER_SIZE );
if ( rx_size > 0 ) {
int32_t buf_cnt = 0;
if ( app_buf_len + rx_size >= PROCESS_BUFFER_SIZE ) {
uartmux2_clear_app_buf( );
return -2;
} else {
buf_cnt = app_buf_len;
app_buf_len += rx_size;
}
for ( int32_t rx_cnt = 0; rx_cnt < rx_size; rx_cnt++ ) {
if ( rx_buff[ rx_cnt ] != 0 ) {
app_buf[ ( buf_cnt + rx_cnt ) ] = rx_buff[ rx_cnt ];
} else {
app_buf_len--;
}
}
return 0;
}
return -1;
}
// ------------------------------------------------------------------------ END