30 min

Simplify data and information visualization with HCMS-3906 and STM32F407ZG

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Dot Matrix R Click with Fusion for ARM v8

Published Sep 07, 2023

Click board™

Dot Matrix R Click

Development board

Fusion for ARM v8


NECTO Studio



Our cutting-edge solution featuring a four-digit red dot matrix display module brings your messages to life with clarity and precision, making information dissemination a breeze



Hardware Overview

How does it work?

Dot Matrix R Click is based on the HCMS-3906, a four-digit dot matrix display module from Broadcom. Dot Matrix R Click is a high-performance, easy-to-use dot matrix display driven by an onboard CMOS IC. Each display can be directly interfaced with a microprocessor, thus eliminating the need for cumbersome interface components. The serial IC interface allows higher character count information displays with a minimum of data lines. The easy-to-read 5x7 pixel format allows the display of upper case, lower case, Katakana, and custom user-defined characters. These displays are stackable in the x- and y-directions, making them ideal for high character count displays. Typical applications include telecommunication equipment, portable data entry devices, computer peripherals, medical equipment, test equipment, business machines, avionics, industrial controls, and more. Featured LED display HCMS-3906 consists of LEDs configured as 5x7 font characters driven in groups of 4 characters per IC. Each IC comprises a 160-bit shift register (the Dot Register), two 7-bit Control Words, and refresh circuitry. The Dot Register contents are mapped on a one-to-one basis to the display. Thus, an individual Dot Register bit uniquely controls a single LED. Reset initializes the Control Registers (sets all Control Register bits to

logic low) and places the display in sleep mode. The Dot Registers are not cleared upon power-on or by Reset. After power-on, the Dot Register contents are random; however, Reset will put the display in sleep mode, thereby blanking the LEDs. The Control Register and the Control Words are cleared to all zeros by Reset. Load the Dot Register with logic lows to operate the display after being Reset. Then, load Control Word 0 with the desired brightness level and set the sleep mode bit to logic high. The Dot Register holds the pattern to be displayed by the LEDs. First, RS is brought low, then CE is brought low. Next, each successive rising CLK edge will shift the data at the DIN pin. Loading a logic high will turn the corresponding LED on; a logic low turns the LED off. When all 160 bits have been loaded, CE is brought to logic high. When CLK is next brought to logic low, new data is latched into the display dot drivers. Loading data into the Dot Register occurs while the previous data is displayed and eliminates the need to blank the display while loading data. In a 4-character display, the 160 bits are arranged as 20 columns by 8 rows. This array can be conceptualized as four 5x8 dot matrix character locations, but only 7 of the 8 rows have LEDs. The bottom row (row 0) is not used. Thus, latch location 0 is never displayed. Column 0 controls the left-most column.

Data from Dot Latch locations 0-7 determine whether or not pixels in Column 0 are turned on or off. Therefore, the lower left pixel is turned on when a logic high is stored in Dot Latch location 1. Characters are loaded serially, with the left-most character loaded first and the rightmost character loaded last. By loading one character at a time and latching the data before loading the next character, the figures will appear to scroll from right to left. The Control Register allows software modification of the IC’s operation and consists of two independent 7-bit control words. Bit D7 in the shift register selects one of the two 7-bit control words. Control Word 0 performs pulse width modulation, pixel map, brightness control, peak pixel current brightness control, and sleep mode. Control Word 1 sets serial/simultaneous data out mode and external oscillator prescaler. Each function is independent of the others. 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.

Dot Matrix R Click top side image
Dot Matrix R Click bottom side image

Features overview

Development board

Fusion for ARM 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 ARM® Cortex®-M based 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, Fusion for ARM v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the Fusion for ARM 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. Fusion for ARM 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.

Fusion for ARM v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M4

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Register Selection
SPI Chip Select
SPI Clock
Power Supply
Display Blank
Power Supply

Take a closer look


Dot Matrix R 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 Fusion for ARM v8 as your development board.

Fusion for PIC v8 front image hardware assembly
Buck 22 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
v8 SiBRAIN 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 Dot Matrix R Click driver.

Key functions:

  • dotmatrixr_set_bl_pin_state - Sets BL pin to high or low state

  • dotmatrixr_restart - Restart device

  • dotmatrixr_write_ascii - Sets display to written value

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 DotMatrixR Click example
 * # Description
 * This demo application show data on display.
 * The demo application is composed of two sections :
 * ## Application Init 
 * Configuration device
 * ## Application Task  
 * Display shows 3 different data in span of 1 second
 * \author MikroE Team
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "dotmatrixr.h"

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

static dotmatrixr_t dotmatrixr;
static log_t logger;

char demo_t1[ 6 ] = "####";
char demo_t2[ 6 ] = "____";
char demo_t3[ 6 ] = "DotR";

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

void application_init ( void )
    log_cfg_t log_cfg;
    dotmatrixr_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.

    dotmatrixr_cfg_setup( &cfg );
    dotmatrixr_init( &dotmatrixr, &cfg );

    Delay_ms( 100 );
    dotmatrixr_restart( &dotmatrixr );
    Delay_ms( 500 );
    dotmatrixr_set_bl_pin_state( &dotmatrixr, 0 );
    dotmatrixr_set_rs_pin_state( &dotmatrixr, 0 );

    dotmatrixr_ctrl_1( &dotmatrixr, DOTMATRIXR_CTRL_BYTE_1_OSC_PRESCALER_1 |
                       DOTMATRIXR_CTRL_BYTE_1_DOUT_DIN );
    dotmatrixr_ctrl_0( &dotmatrixr, DOTMATRIXR_CTRL_BYTE_0_BRIGHTNESS_30 |
                       DOTMATRIXR_CTRL_BYTE_0_PIXEL_PEAK_CURRENT_9p3mA |
                       DOTMATRIXR_CTRL_BYTE_0_MODE_NORMAL );

void application_task ( void )
    dotmatrixr_write_ascii( &dotmatrixr, &demo_t1[ 0 ] );
    Delay_ms( 1000 );
    dotmatrixr_write_ascii( &dotmatrixr, &demo_t2[ 0 ] );
    Delay_ms( 1000 );
    dotmatrixr_write_ascii( &dotmatrixr, &demo_t3[ 0 ] );
    Delay_ms( 1000 );

void main ( void )
    application_init( );

    for ( ; ; )
        application_task( );

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

Additional Support