SPI display offers a low-cost, low-power solution for showing text and graphics. They require fewer pins than traditional Parallel interfaces and simplify the interface to microcontrollers with limited I/O pins.
In this article, you will learn about this interface, including the following:
- What the SPI interface is
- Differences between its 3-wire and 4-wire modes
- What devices use it
- Benefits of SPI displays
- Limitations of SPI displays
- SPI displays types you can select
After reading this guide, you will know how to find the right SPI display module for your products. And it will be easier to develop your project with Arduino or Raspberry PI.
What is SPI Interface?
SPI (Serial Peripheral Interface) is a standard interface developed by Motorola. It is used by MCU (microcontroller or Microcontroller Unit) and other devices to connect to sensors, storage cards, displays, and other peripherals.
A standard SPI uses 3 simple wires:
- A data wire to send data from the MCU to the peripheral (MOSI)
- A wire to send data from the peripheral to the IC (MISO).
- A separate serial clock line (SCLK) wire to tell the devices when to send or read data.
SPI works over short distances and uses a master-slave setup. The master device controls the clock, initiates sending and receiving data, and terminates communication. The slaves receive data and clock signals from the master.
It uses a synchronous serial protocol, keeping the master and slaves precisely synchronized to the clock signal.
Sometimes an extra Chip Select (SS) wire is used to choose which peripheral will send/receive data. That is 4-wire SPI interface mode.
Differences between 3-wire and 4-wire SPI interface
SPI Interface comes in 3-wire or 4-wire version. The 3-wire SPI uses 3 basic wires:
- MOSI – Master Out, Slave In
- MISO – Master In, Slave Out
- SCLK – Separate Serial Clock. It provides a clock signal that tells both the master and slave when to send or receive data.
3-wire SPI allows a single master device to communicate with one slave device at a time. The slave device can be a sensor, memory chip, or LCD screen.
4-wire SPI adds a fourth wire, typically called SS (Slave Select) or CS (Chip Select). This wire lets the master select which slave device should send or receive data.
With a 4-wire SPI, the master can quickly switch between multiple slave devices connected to the same SPI bus. This allows connecting multiple slave devices to the same SPI bus.
Even though 4-wire SPI uses more wires, it gives you more options for linking various components. 3-wire SPI uses less pins but is limited to a single master-slave link.
Some specific uses
- 3-wire SPI: Connecting a sensor, memory chip, mini display, etc.
- 4-wire SPI: Connecting multiple sound chips, several displays, large external memories, microSD cards, touch panels, etc.
In short, 4-wire SPI adds chip-selecting ability through the SS wire. That allows the SPI master to dynamically switch between and communicate with multiple SPI slaves on the same set of wires.
3-wire SPI and 4-wire SPI work similarly. They share a clock and data in-and-out lines, and both use the same communication protocols. Many SPI devices actually support both 3-wire and 4-wire modes.
Common uses of SPI Interface
SPI is a simple, flexible and widely adopted serial interface standard. That makes it useful for connecting many types of accessories to MCUs. Examples are:
Connecting screens to MCUs.
Interfacing sensors (pressure, temperature, light, motion, etc.).
Many sensors use SPI Interface to transmit analog or digital data to an MCU.
Connecting external memory (NOR Flash, NAND Flash, SD cards).
SPI is the normal way to connect to serial memory devices like these.
Inter-chip communication between multiple devices on a board.
Using a common clock and CS/SS signal, two devices can communicate over an SPI bus.
Upgrading to other serial standards.
Most of the time, it’s easy to change the SPI interface to faster standards like MIPI, which uses a similar serial protocol style. That offers potential for future upgrades and enhancements.
SPI is a simple, flexible and widely adopted serial interface standard. That makes it useful for connecting many types of peripherals to MCUs.
Learn about the key features and benefits of SPI. That helps you decide when it’s a good choice to connect sensors, storage, displays, or other devices to your designs.
Benefits of SPI Displays
SPI displays offer some great benefits, including:
- Smaller, cheaper connectors and cables
- Less noise and interference for better picture quality
- More flexible speed control and power management
- Lower interface implementation costs
- Easy upgrades to better interfaces in the future
Smaller, cheaper connectors and cables
SPI only needs 3 wires (MOSI, MISO, SCLK) compared to more wires for other interfaces (like Parallel). This led to smaller connectors and thinner cables, which helped mobile devices save space and cost less.
Less noise and interference for better picture quality
SPI reduces EMI (Electromagnetic interference) or “crosstalk” since it sends data across one wire at a time rather than simultaneously across multiple wires. So, it gives cleaner signals and better-quality video output.
More flexible speed control and power management
SPI also provides more flexibility. With SPI, the master device can:
- pause the clock for a break
- change clock speeds dynamically based on needs
- cycle power on and off automatically.
That helps improve battery life, which is important for mobile display devices.
Lower interface implementation costs
Additionally, SPI tends to be simpler and cheaper to implement than other interfaces. This helps keep costs down, especially when producing fewer items.
Easy upgrades to better interfaces in the future
Also, it is easy to switch it to a faster interface like MIPI DSI, which is similar to SPI. That means it has an easy path to future improvements, which makes the design last longer and be more useful.
Because of these benefits, SPI is a great choice for mini and small screens where its bandwidth limits are enough. Generally, it would be best to have a faster, dedicated interface for larger, higher-resolution displays.
But it can potentially serve as a starting point. It is a simple, space-saving, flexible, and cheap solution to link displays. It also has the power to upgrade to meet new needs as time passes.
Limitations of SPI Displays
SPI only provides a 3-wire serial interface, so it has some limitations for connecting larger or more advanced displays.
Display Resolution and Pixel Density
SPI cannot send data fast enough for full-color, high-resolution displays with lots of pixels.
Its top speed is around 50 MHz, so screens are limited to around QVGA (320×240) resolution with basic colors. The biggest SPI TFT LCD display in our products list is the 3.5-inch screen with a 320×240 resolution. Bigger and Higher resolution displays require faster interfaces like RGB, MIPI and LVDS.
Display Commands and Control Over SPI
SPI simply sends pixel data; it cannot transmit display commands or instructions. That means it requires a separate interface for tasks like:
- moving the cursor,
- clearing the screen,
- changing the backlight,
- drawing shapes/text,
Managing the screen’s logic and commands makes things more complicated.
Display-Specific Encoding and Format
SPI is purely a serial data link interface. It does not use any special display formatting or encoding. It just sends pixel data as a series of numbers. So pixel data must be formatted separately for sending over SPI.
Because of this, different types of displays require different ways to deal with data. That results in different display types required in different ways. SPI itself cannot handle display-specific encoding and transmission.
Limited driver support makes SPI signals more likely to be affected by EMI or “crosstalk” over long distances. While fine for short links, display cables often require extra shielding, buffers or line drivers to address signal issues properly.
This adds cost and complication. So, we usually use high-quality metal SPI lines and proper termination for signal integrity.
In summary, SPI is good for mini and simple displays. Where its limitations are minimal and do not affect the user experience. However, it cannot truly replace dedicated high-speed display interfaces for larger or more advanced needs.
Other interfaces provide key advantages like:
- Much faster speeds and greater bandwidth for big, high-quality displays
- Sending display commands and logic instructions for full control
- Using display-specific encoding and protocols for optimal pixel data transmission
- Integrated solutions to manage EMI/crosstalk and properly drive signals over longer distances
For simple prototypes or proofs-of-concept, SPI can work well for mini displays. But for high-end screens, we need a more robust dedicated interface.
Examples of SPI displays
SPI supports a few types of mini, lower-cost displays well. Screens like:
Mini monochrome, color and backlit text displays
Small character LCDs commonly have dimensions like 16×2, 20×4, etc. These are ideal for basic text output and are available in monochrome, color and LED-backlit variations.
Small PMOLED displays
PMOLED display modules (up to 3 inches) provide SPI interfaces for basic monochrome output. And PMOLED screens can provide a high contrast ratio and wide viewing angles. Some examples are the SSD1306, SH1106, etc.
Basic QVGA (320×240) TFT LCDs
Some QVGA SPI LCDs provide SPI interfaces for simple graphics and interfacing touch screens (like resistive touch screens). But bandwidth limits make SPI display only available in low resolutions. Our TFT LCD modules have some screens like the 1.3 TFT display, 2.4 TFT display, etc
Mini monochrome or color e-Ink displays also use the SPI interface. They provide permanent display until intentionally refreshed. They can be used for applications like price tags, name badges, labels, etc. Examples include the e-Paper series.
In summary, SPI caters to small displays for basic needs. Screen types cover monochrome/color characters, small graphics, OLEDs and e-Paper for development, testing, education and more.
In conclusion, SPI (Serial Peripheral Interface) is a simple and useful serial communication protocol. It uses a clock signal to keep everything in sync. SPI comes in 3-wire and 4-wire versions.
The 3-wire version lets one master device talk to one slave. The 4-wire version lets the master switch between multiple slaves.
SPI is popular for connecting small displays, sensors, memory chips, and other peripherals to MCU. It’s cheap, reduces noise, lets you control the speed, and saves space.
However, SPI is too slow for large, high-resolution displays and needs to do more to control a screen fully.
It works great for small, basic displays and simple components. But you’ll want a faster interface to do more for high-performance applications.
Overall, SPI gives a simple, compact way to link various ICs and components for development, testing, and low-end embedded systems.
In short, SPI is an easy-to-use serial interface for connecting microcontrollers to small, basic peripherals. It’s limited but useful, especially for a small, cheap solution.
For anything more advanced, a faster interface is needed. But SPI is a great place to start!