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Communication with a 7-segment display via SPI


This article explores the application of the SPI protocol with SmartWave, showcasing its usage with a 7-segment display module. It provides insights into the fundamentals of the SPI communication protocol and illustrates the seamless configuration of an SPI driver interface to control a 7-segment display using SmartWave through our WebGUI.

7-segment display module

Used SPI Protocol

The Serial Peripheral Interface (SPI) stands out as one of the most frequently employed interfaces for connecting a microcontroller to peripherals like ADCs, DACs, and various other sensors.  This segment aims to emphasize key aspects of SPI and its application with SmartWave. For an in-depth understanding of the SPI protocol, readers are encouraged to explore the following article from Analog Devices.

SPI operates as a synchronous, full-duplex interface between the main device and peripherals. Data synchronization occurs on either the rising or falling clock edge, allowing simultaneous data transmission from both the main and subnode. The SPI interface offers flexibility, supporting configurations of either 3-wire or 4-wire setups. 

The device responsible for generating the clock signal is termed the "main". Data exchanged between the main and subnode aligns with the clock signal generated by the main device. Notably, SPI devices boast significantly higher clock frequencies when compared with I2C interfaces. While SPI interfaces can accommodate multiple subnodes, it's essential to note that, unlike I2C, SPI supports only a single main device.

A standard SPI setup between a main and a subnode appears as follows.

Basic SPI communication link

The 4-wire SPI devices have the following four signals:

  • Clock (SCLK, SPI CLK)

  • Main Out - Subnode In (MOSI)

  • Main In - Subnode Out (MISO)

  • Chip Select (CS)

Initiating SPI communication requires the main device to transmit the clock signal and designate the subnode by activating the CS signal. The serial clock edge coordinates the shifting and sampling of data. SPI, operating as a full-duplex interface, allows simultaneous transmission and reception of data through the MOSI and MISO lines, respectively. Users can configure the Clock Phase and Clock Polarity, determining how data is sampled and shifted.

SPI Data Transmission


The 7-segment display, in this demonstration, is powered by the MAX7219 serial input/output common-cathode display driver from Maxim Integrated. The simplified schematic below illustrates how to establish the connection between SmartWave and the display driver module. This configuration employs 3-wire SPI communication, as data is only transmitted from the main device (SmartWave), and no data is received from the subnode. Additionally, the inclusion of Vdd and GND lines is necessary to power the display driver module.

Simplified block diagram

How to Use SmartWave

Setting up the SPI communication has never been easier with our user-friendly WebGUI interface, where everything can be configured with ease. Upon selecting the SPI driver, the user have the option to configure the Clock Phase, Clock Polarity, Chip Select polarity, clock frequency, and the bit width. SmartWave also offers 16 GPIOs. Using the pin layout shown in the bottom right corner, users can easily choose which pins to use for SPI communication. The SCLK, MOSI, and CS pins are configured in a push-pull setup, while MISO is left open when no subnode is connected or can be switched to pull-up when this line is used. Before initiating the SPI protocol, users have to specify the data they want to transmit and choose an appropriate sampling frequency. Once everything has been set up, and all the lines are connected to the target device, users can initiate communication either by pressing the trigger button on SmartWave or through the WebGUI.

SmartWave WebGUI setup

7-Segment Demo

To run our demo, upload the "SPI_7SEGMENT.json" configuration file from our GitHub repository to the WebGUI. This pre-configured file facilitates 3-wire SPI communication, displaying the "HELLO" string on the 7-segment display. Before starting the demo, ensure that SmartWave is connected to the PC and selected in the WebGUI. Display "HELLO" on the 7-segment module by either pressing the trigger button on SmartWave or transmitting it through the WebGUI interface. No further configuration is required.

Hardware setup


This short demonstration covered the basics of the SPI communication protocol and exemplifies the simplicity and effectiveness of SmartWave in leveraging SPI communication for diverse applications.

For those looking to unlock the potential of SmartWave in their projects, we encourage reaching out to semify via email ( for additional details, product demonstrations, or to discuss specific requirements. You can also explore other interesting articles and demos featuring SmartWave through the following links.

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