30 min

Bridge the gap between RS232 and SPI interfaces using MAX3100 and PIC32MX764F128L

From RS232 to SPI: A revolution in data transformation

RS232 SPI Click with UNI-DS v8

Published Oct 19, 2023

Click board™

RS232 SPI Click

Development board



NECTO Studio



Effortlessly convert RS232 data into the SPI format with our user-friendly solution, streamlining the process of modernizing data communication



Hardware Overview

How does it work?

RS232 SPI Click is based on two ICs - MAX3100 and MAX3232. The MAX3100 serves as UART interface to the SPI/MICROWIRE compatible interface converter. In the same time, MAX3232 device enables RS232 SPI click to meet the requirements of TIA/EIA-232-F and also provides the electrical interface between an asynchronous communication controller and the serial-port connector. The charge pump and four small external capacitors allow operation from a single 3-V to 5.5-V supply. RS232 SPI click Uses an SPI™/MICROWIRE™ interface for communication with the host microcontroller (µC). Then, the MAX3100 is responsible for conversion from synchronous serial data from a microcontroller to asynchronous, serial-data communication port such as RS-232, RS-485, IrDA. In this case the

RS232 protocol is used. The MAX3100 includes a crystal oscillator and a baud rate generator with software-programmable divider ratios for all common baud rates from 300 baud to 230k baud. The transmitter section accepts SPI/MICROWIRE data, formats it, and transmits it in asynchronous serial format from the TX output. Data is loaded into the transmit buffer register from the SPI/MICROWIRE interface. The MAX3100 adds start and stop bits to the data and clocks the data out at the selected baud rate. A software- or hardware-invoked shutdown lowers quiescent current to 10µA, while allowing the MAX3100 to detect receiver activity. An 8-word-deep first-in/first-out (FIFO) buffer minimizes processor overhead. This device also includes a flexible interrupt with four maskable sources, including address recognition

on 9-bit networks. Two hardware-handshaking control lines are included (one input and one output). Because of the features contained in its modules, the RS232 SPI click can be used for handheld instruments, UART in SPI systems, small networks in HVAC or Building control, battery-powered systems, PDAs, notebooks and many more. 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.

RS232 SPI Click top side image
RS232 SPI Click bottom side image

Features overview

Development board

UNI-DS v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different STM32, Kinetis, TIVA, CEC, MSP, PIC, dsPIC, PIC32, and AVR MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, UNI-DS v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the UNI-DS v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector. Communication options such as USB-UART, USB

HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. UNI-DS v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

UNI-DS v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation



MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


You complete me!


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 SPI Click accessories image

Used MCU Pins

mikroBUS™ mapper

SPI Chip Select
SPI Clock
Power Supply
Power supply

Take a closer look


RS232 SPI Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI-DS v8 as your development board.

Fusion for PIC v8 front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
v8 SiBRAIN 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 Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for RS232 SPI Click driver.

Key functions:

  • rs232spi_reg_write - This function writes two bytes of data using the SPI serial interface.

  • rs232spi_reg_read - This function reads two bytes of data using the SPI serial interface.

  • rs232spi_digital_write_rst - This function writes the specified digital signal to the RST pin.

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * \file 
 * \brief Rs232Spi Click example
 * # Description
 * This example showcases how to initialize and use the RS232 SPI click. The click has a uni-
 * versal asynchronous transceiver which uses a SPI serial interface to communicate with the 
 * MCU. In order for this example to work, 2 clicks are needed - a receiver and a transmitter.
 * The demo application is composed of two sections :
 * ## Application Init 
 * This function initializes and configures the logger and click modules. Additional configura-
 * ting is done in the default_cfg(...) function.
 * ## Application Task  
 * This function receives and displays UART data in the "read mode" and sends the predefined 
 * message in the "write mode".
 * \author MikroE Team
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "rs232spi.h"

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

static rs232spi_t rs232spi;
static log_t logger;

static const uint8_t message[ 9 ] = { 'M', 'i', 'k', 'r', 'o', 'E', 13, 10, 0 };

static const uint8_t RX_MODE = 1;
static const uint8_t TX_MODE = 0;

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

void application_init ( )
    log_cfg_t log_cfg;
    rs232spi_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.

    rs232spi_cfg_setup( &cfg );
    rs232spi_init( &rs232spi, &cfg );
    Delay_ms( 100 );
    rs232spi_digital_write_rst( &rs232spi, 1 );
    Delay_ms( 100 );
    rs232spi_default_cfg( &rs232spi, 115200 );
    Delay_ms( 100 );
    rs232spi_flush( &rs232spi );
    Delay_ms( 100 );
    log_printf( &logger, "App init done...\r\n" );

void application_task ( )
    uint8_t mode = RX_MODE;
    uint8_t cnt;
    char txt;

    if ( mode == RX_MODE )
        if ( rs232spi_data_ready( &rs232spi ) != 0 )
            txt = rs232spi_transfer( &rs232spi, RS232SPI_CMD_READ_DATA );
            log_printf( &logger, "%c", txt );
    else if ( mode == TX_MODE )
        for ( cnt = 0; cnt < 9; cnt++ )
            rs232spi_data_write( &rs232spi, message[ cnt ] );
            Delay_ms( 500 );

void main ( )
    application_init( );

    for ( ; ; )
        application_task( );

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

Additional Support