Table of Contents
Introduction
LCD display modules rely on a range of internal and external interfaces to work properly and communicate with other devices. Before diving into the detail of LCD interfaces’ technical background, practical applications and limitations, let’s clear up the easily mixed up concepts of interface and protocol.
Distinguishing Between TFT Display Interface and Protocol
Interface and protocol serve distinct functions in communication, especially for LCD displays:
Interface refers to the hardware configuration enabling two or more devices to connect physically.
Protocol dictates how data moves across the interface, outlining data structure, rules, and mechanisms for error detection and correction.
A simple example of interface & protocol is two people chatting face to face. They communicate through vibrated air (interface), using English as protocol.
Internal LCD Interfaces for Display Modules
Internal interfaces are foundation of LCD operation, allowing internal components like the controller and display drivers to communicate seamlessly. These interfaces fall into Universal and Image Transfer categories.
Universal Internal LCD Interfaces
Universal interfaces allow control command and image data to be transmitted. Each has unique properties and use cases, detailed below.
1. SPI (Serial Peripheral Interface)
– Overview: SPI was developed in the 1980s by Motorola for quick, synchronous data transfer, focusing on efficiency and simplicity. It’s a full-duplex communication protocol where data is sent and received simultaneously, making it ideal for high-speed applications. The interface uses four main lines: MOSI (Master Out Slave In), MISO (Master In Slave Out), SCK (Serial Clock), and SS (Slave Select).
– Technical Characteristics: SPI is known for clocking speeds reaching up to 10 Mbps or more, allowing for rapid data transfer. Because SPI is a master-slave protocol, the master initiates all communication, keeping system design straightforward.
– Applications: SPI is widely used in high-refresh-rate displays, where quick data exchange is necessary, such as in embedded systems with limited space for wiring.
– Advantages: Fast communication speed and simplicity make SPI suitable for real-time data transmission in compact, high-speed devices.
– Limitations: Requires more wiring, especially when multiple devices share the bus, as each device needs a dedicated slave-select line.
2. I2C (Inter-Integrated Circuit)
– Overview: Developed by Philips Semiconductors in the early 1980s, I2C is a two-wire communication protocol designed for simple, low-speed data exchange between components on a single board. I2C is a multi-master, multi-slave protocol that’s highly popular in electronic devices.
– Technical Characteristics: Using two wires, SDA (data) and SCL (clock), I2C supports a maximum standard speed of 400 kHz, with a high-speed mode capable of reaching 3.4 MHz. I2C’s simplicity and flexibility make it a cost-effective choice.
– Applications: Common in displays where multiple peripherals must share a single bus, I2C is often used for sending configuration commands and low-speed data, like touchscreen data.
– Advantages: Low wiring requirements and support for multiple devices make I2C highly efficient and space-saving.
– Limitations: Limited by slower data speeds compared to SPI, making it unsuitable for applications requiring high-frequency data transfer.
4. UART (Universal Asynchronous Receiver/Transmitter)
– Overview: UART predates most serial communication standards and is widely integrated into micro-controllers. UART supports asynchronous data transmission, eliminating the need for a shared clock line.
– Technical Characteristics: Each UART chip transmits data serially with start and stop bits that frame each byte, allowing data to be synchronized without a clock. UART speeds vary, typically between 9600 bps and 115200 bps.
– Applications: Commonly used in embedded systems for communication with peripherals, UART is compatible with text-based displays where real-time data isn’t critical.
– Advantages: Simple, asynchronous communication for short distances.
– Limitations: Slower and less synchronized than other protocols, such as SPI or I2C, which may affect applications needing high-speed data transmission.
Internal Image Transfer LCD Interfaces
Image transfer interfaces manage high-bandwidth data transmission, essential for the display’s image quality and response rate.
1. LVDS (Low-Voltage Differential Signaling)
– Overview: LVDS was developed in the 1990s as a low-power, high-speed digital interface that minimizes electromagnetic interference (EMI). LVDS sends data over twisted-pair cables using low-voltage differential signaling. There are several variants (18bit, 24bit VESA, 24bit JEIDA) on LVDS implementations. They are not fully compactible with each other.
– Technical Characteristics: LVDS transmits data at rates exceeding 2 Gbps and is highly noise-resistant, making it suitable for environments with high EMI.
– Applications: LVDS is standard in industrial displays, automotive applications, and large-screen TVs due to its ability to handle large data volumes over relatively long distances.
– Advantages: High data rate and resistance to EMI.
– Limitations: Complex wiring and cost can increase, making it less suitable for low-budget applications.
2. RGB
– Overview: RGB transmission, using the three primary color channels (Red, Green, and Blue), originated with CRT monitors and has been adapted for use in LCDs, mainly in simpler displays.
– Technical Characteristics: RGB is a special kind of parallel interface. It requires no display RAM. MCU directly updates the TFT screen, by transmitting color data for each pixel across multiple wires, with separate lines for each color channel. Pixel data is synchronized with a clock pulse to ensure proper timing.
– Applications: RGB is prevalent in low-resolution displays and older devices, where advanced data transfer capabilities aren’t required.
– Advantages: Cost-effective and simple to implement.
– Limitations: Limited speed and resolution support, making it impractical for modern high-definition displays.
3. MIPI (Mobile Industry Processor Interface)
– Overview: Developed by the MIPI Alliance, MIPI has two sub-categories, DSI (Display Serial Interface) and CSI (Camera Serial Interface). It is a standardized interface optimized for high-speed data transfer in mobile and portable devices. The interface supports high data rates with low power consumption and EMI (electromagnetic interference).
– Technical Characteristics: MIPI DSI uses differential signaling with low power and high-speed modes, making it efficient in moving large amount of data between processor and display module. MIPI DSI supports two working modes:
Command Mode: Used for sending control commands to the display.
Video Mode: Optimized for continuous data streaming.
– Applications: Commonly used in mobile phones, tablets, and portable devices due to its efficiency and compact footprint.
– Advantages: High data rate (up to 6Gbps), power efficiency, low EMI and compact size.
– Limitations: Limited cable length and complexity make MIPI unsuitable for larger, non-portable applications.
4. Vx1
– Overview: Vx1, or V-by-One HS, is a high-speed serial interface standard developed by THine Electronics. It is designed to handle extremely high data rates, such as those required for 4K and 8K displays.
– Technical Characteristics: Vx1 can reach speeds up to 4 Gbps per channel, enabling the transmission of large image files quickly and efficiently.
– Applications: Found in high-end TVs, professional displays, and signage where 4K or 8K resolution is standard.
– Advantages: Ultra-fast data rates suited for high-resolution displays.
– Limitations: High cost and complexity limit Vx1’s practicality in smaller or simpler displays.
5. eDP (Embedded Display Port)
– Overview: Embedded Display Port (eDP) is an internal interface derived from Display Port technology, designed specifically for high-resolution displays in laptops and tablets and other portable devices, offering significant advantages over older standards like LVDS.
– Technical Characteristics: eDP supports high data rates (up to 8.64Gbps) and advanced features like variable refresh rates, which improve power efficiency and extend battery life in portable devices.
– Applications: eDP is widely used in laptops and tablets, providing a high-quality display experience while balancing power consumption and using less wire (compared to LVDS).
– Advantages: High resolution, power efficiency, and support for adaptive refresh rates.
– Limitations: Complexity and higher cost may be excessive for simpler applications.
Here’s a comparison of common internal image transfer interfaces—LVDS, RGB, MIPI DSI, Vx1, and eDP—highlighting their respective features, advantages, and drawbacks. These interfaces are used within devices to transfer data between the controller and the LCD module and are selected based on factors like resolution, power efficiency, cable length, and EMI resistance.
| Feature | LVDS | RGB | MIPI DSI | Vx1 | eDP |
|---|---|---|---|---|---|
| Typical Application | Industrial, automotive displays | Older displays, budget applications | Mobile devices, tablets, laptops | High-performance TVs, monitors | Laptops, high-resolution monitors |
| Max Resolution | 1080p | 720p | Up to 4K | 8K | 8K (depends on version) |
| Max Refresh Rate | 60Hz | 60Hz | Up to 120Hz | 60 Hz (higher with multiple lanes) | 60~120Hz |
| Data Rate | ~2.98 Gbps | ~40 Mbs | Up to 10 Gbps | Up to 16 Gbps per channel | Up to 77.4 Gbps (eDP 2.0) |
| Signal Type | Differential (digital) | Analog (parallel) | Differential (digital serial) | Differential (digital serial) | Differential (digital serial) |
| Data Lanes | 2 to 8 | Up to 24 channels | 1 to 4 | 1 to 8 | 1 to 4 (expandable with HBR modes) |
| Power Consumption | Moderate | Low | Low | Moderate | Moderate to high |
| Cable Length | Moderate (up to 10m with quality loss) | Short | Short (centimeters to inches) | Moderate | Short to moderate (internal use) |
| EMI Tolerance | High | Low | Moderate | High | High |
| Scalability | Limited | Limited | High | High | High |
Summary of Each Internal LCD Interface's Best Applications
LVDS: Ideal for industrial and automotive applications due to its EMI resistance and moderate power consumption. However, it lacks the scalability required for high-resolution displays.
RGB (Parallel): Best for legacy or budget applications with lower resolution requirements, as it is low-cost but limited in scalability and resolution capabilities.
MIPI DSI: Suited for mobile devices, tablets, and some laptops due to its low power consumption, moderate EMI resistance, and support for high resolutions up to 4K. Its short-distance transmission is ideal for compact devices.
Vx1: Designed for high-performance TVs, monitors, and large displays, supporting high resolutions (up to 8K) and moderate cable lengths. It combines high data rates with good EMI resistance, making it suitable for professional and commercial displays.
eDP: Commonly used in laptops and professional monitors due to its support for high resolutions, adaptive refresh rates, and moderate EMI resistance. It offers scalability for modern, high-resolution displays, though it may require more power for higher resolutions.
External LCD Interfaces for Display Modules
External interfaces are essential in connecting LCD display modules with external sources, such as industry control devices, computers, gaming consoles, media players, and mobile devices. They facilitate the transmission of video and sometimes audio data, ensuring high-quality output tailored to various application needs. This section will cover key external interfaces: USB-C, HDMI, DVI, RGB (VGA), and DisplayPort (DP).
USB-C (Universal Serial Bus Type-C)
– Overview: USB-C has revolutionized connectivity by combining power, data, and video transmission in a single, compact port. Developed by the USB Implementers Forum and launched in 2014, USB-C has quickly become the standard in modern devices due to its reversible design and versatility, supporting data rates up to 10 Gbps with USB 3.1 and even up to 40 Gbps with Thunderbolt 3 and 4. USB-C ports also support Display Port Alternate Mode, which enables video signal transmission to an external display.
– Technical Characteristics: With Display Port Alt Mode, USB-C can handle video resolutions up to 8K at 60 Hz. The port supports power delivery (PD), allowing devices to charge while transmitting video data, which is essential for compact devices like laptops and tablets. Display Port over USB-C supports Multi-Stream Transport, enabling multiple displays to be connected through a single port, which is beneficial for multi-monitor setups.
– Applications: USB-C is widely used in laptops, tablets, and smartphones that require minimalistic, multi-purpose connectivity. It’s particularly beneficial in thin and light devices due to its small size and high power throughput, often eliminating the need for separate power and video cables.
– Advantages:
Multi-functionality (supports video, power, and data).
High data transfer and charging capabilities.
Reversible design for ease of use.
– Limitations:
Limited compatibility with non-USB-C devices unless adapters are used.
Alt Mode variations (such as DisplayPort and Thunderbolt) can create compatibility confusion, as not all USB-C ports support video output.
HDMI (High-Definition Multimedia Interface)
– Overview: HDMI was introduced in 2003 as a digital successor to analog interfaces like VGA and RCA. Developed by a consortium of technology companies, HDMI was designed to simplify and improve the quality of connections between multimedia devices by transmitting uncompressed digital audio and video. Over the years, HDMI has evolved through several versions (e.g., HDMI 1.4, 2.0, 2.1), each increasing data bandwidth, supporting higher resolutions, refresh rates, and audio channels.
– Technical Characteristics: HDMI 2.1, the latest version, supports resolutions up to 10K at 120 Hz, with bandwidth up to 48 Gbps. HDMI cables also come with HDCP (High-bandwidth Digital Content Protection) for secure content transfer, essential for streaming and digital media players.
– Applications: HDMI is the standard interface for home entertainment systems, including TVs, gaming consoles, projectors, and audio/video receivers. Its ability to handle both video and audio in a single cable makes it an easy choice for consumer electronics.
– Advantages:
High-quality, uncompressed video and audio.
Widely compatible across consumer electronics.
Supports additional features like CEC (Consumer Electronics Control) for controlling multiple devices through a single remote.
– Limitations:
HDMI cables can be thick and less flexible, making them harder to manage in some setups.
The length limitation for HDMI cables can affect use in larger installations, while displays reside a bit farther away from main machines.
DVI (Digital Visual Interface)
– Overview: DVI was introduced in 1999 as a bridge between older analog interfaces and newer digital connections, primarily for computer monitors. DVI comes in several versions: DVI-A (analog-only), DVI-D (digital-only), and DVI-I (integrated, supporting both analog and digital). DVI can transmit uncompressed digital video but lacks support for audio transmission.
– Technical Characteristics: DVI-D and DVI-I support video resolutions up to 1920×1200 at 60 Hz, with Dual-Link DVI supporting up to 2560×1600. DVI uses TMDS (Transition Minimized Differential Signaling) for data transmission, which reduces signal degradation over distance.
– Applications: DVI is common in older computer monitors, projectors, and some legacy video equipment. Although largely replaced by HDMI and DisplayPort, DVI remains a standard in many corporate environments due to its robust performance and simplicity.
– Advantages:
Reliable video quality and backward compatibility with VGA.
Dual-Link DVI supports higher resolutions than typical single-link interfaces.
– Limitations:
No audio support, requiring a separate cable for sound.
Bulkier connectors and limited to short cable lengths without repeaters or boosters.
RGB (VGA)
– Overview: VGA, or Video Graphics Array, was introduced by IBM in 1987 and uses an analog RGB signal for video transmission. The VGA interface consists of a 15-pin connector and transmits analog signals for red, green, and blue channels, each represented by varying voltages.
– Technical Characteristics: VGA supports resolutions up to 640×480 at 60 Hz, but some implementations allow higher resolutions (up to 1080p) with degradation in image quality due to analog signal limitations. VGA’s reliance on analog transmission makes it highly susceptible to interference, resulting in lower image fidelity compared to digital interfaces.
– Applications: VGA is still found in legacy equipment, older PCs, and projectors that support analog input. It is also commonly used in industrial environments and some low-cost monitors.
– Advantages:
Simple and widely recognized interface for legacy compatibility.
Effective for low-resolution video in older devices or certain industrial applications.
– Limitations:
Limited resolution and signal degradation over longer distances.
Susceptible to interference and cannot transmit audio.
DP (Display Port)
– Overview: Display Port, developed by VESA (Video Electronics Standards Association) and released in 2006, was designed as a high-performance digital display interface. Display Port’s primary goal was to replace DVI and VGA by supporting high-resolution displays, multi-monitor setups, and advanced audio features. The interface has undergone several iterations, with the latest Display Port 2.0, supporting incredible data rates and high resolutions.
– Technical Characteristics: Display Port 2.0 supports resolutions up to 16K at 60 Hz or 8K at 120 Hz, with a maximum data rate of 80 Gbps. Display Port uses Micro-Packet Architecture, which enables better data efficiency and makes it highly suitable for video and data-intensive applications like gaming and video production. Display Port connectors also support daisy-chaining, allowing multiple monitors to connect through a single port.
– Applications: Display Port is popular in professional settings, including multi-monitor setups, gaming monitors, and high-resolution professional displays. Its support for Adaptive Sync (for variable refresh rates) also makes it the interface of choice for gaming applications.
– Advantages:
High data rates, suitable for ultra-high-resolution displays.
Supports multiple monitors via daisy-chaining.
Compatibility with both audio and video data.
– Limitations:
Cables are often more expensive than HDMI.
Limited adoption in consumer electronics compared to HDMI.
Comparison of external TFT LCD interfaces:
| Feature | USB-C | HDMI | DVI | RGB (VGA) | Display Port |
|---|---|---|---|---|---|
| Year Introduced | 2014 | 2003 | 1999 | 1987 | 2006 |
| Primary Use Cases | Laptops, tablets, mobile devices | Consumer electronics, industry control | Computers, legacy monitors | Legacy monitors, industrial equipment | High performance displays, gaming |
| Max Resolution & refresh rate | Up to 8K at 60Hz | Up to 10K at 120Hz | Up to 2560×1600 (dual DVI) | Up to 1080p | Up to 16K at 60Hz |
| Data Transfer Rate | Up to 40Gbps | Up to 48Gbps | Up to 9.9Gbps | N/A | Up to 80Gbps |
| Audio Support | Yes | Yes | No | No | Yes |
| Cable Length | Shorter(<2m for best video quality) | Up to 15m for 1080p(HDMI 1.4); 3m for HDMI 2.1 | Up to 5m | Up to 10m or more (with degradation) | 3m or up to 15m with lower resolution |
| Multi-display | Limited(via hubs) | Limited(requires multi-outputs) | No | No | Yes(support daisy-chain) |
| Power Delivery | Up to 100W | No | No | No | No |
| Cable Complexity | Compact and reversible | Moderate(19 pins) | Bulkier(up to 29 pins) | Simple(15 pins) | Moderate(20 pins) |
| Cost | Medium to high | Medium | Low to medium | Low | Medium to high |
Summary
This detailed overview of LCD display interfaces highlights the importance of choosing the right technology for each application. Internal interfaces like SPI, I2C, and UART offer efficient, low-power communication for data transmission within the device, while image transfer interfaces like LVDS, MIPI, and eDP ensure high-quality visual performance in a variety of applications, from portable devices to industrial displays. On the other hand, external interfaces such as USB-C, HDMI, and Display Port allow seamless integration with external sources, supporting high-definition content across entertainment, professional, and gaming environments.
The choice of interface depends on the device’s specifications, intended use, and environmental requirements. Menco offers full range of Tianma TFT LCD product. Our engineers have in-depth know-how of choosing the right interface for your display project. As technology advances, we are likely to see further consolidation around a few highly versatile, high-performance standards, simplifying connectivity across diverse applications while meeting the demands of increasingly sophisticated displays.