Understanding LVDS and RGB

Oct 13, 2025 by wbrum.org 42 views

Introduction

The AM625 System-on-Chip (SoC) from Texas Instruments is a popular choice for Single-Board Computers (SBCs) due to its high-performance capabilities and low power consumption. One of the key features of the AM625 SoC is its ability to output display data in LVDS (Low-Voltage Differential Signaling) format. However, not all displays support LVDS output, and in such cases, converting the LVDS output to RGB (Red, Green, Blue) format becomes necessary. In this article, we will discuss the process of converting LVDS display output to RGB for the AM625 SBC.

Understanding LVDS and RGB

Before we dive into the conversion process, it's essential to understand the basics of LVDS and RGB.

LVDS (Low-Voltage Differential Signaling)

LVDS is a high-speed, low-voltage signaling technology used for transmitting digital data between devices. It uses a differential signaling scheme, where two complementary signals are transmitted over a single wire pair. LVDS is commonly used in display applications, such as LCDs and OLEDs, due to its high-speed data transfer capabilities and low power consumption.

RGB (Red, Green, Blue)

RGB is a color model used to represent colors on a display device. It uses three primary colors - red, green, and blue - to create a wide range of colors. RGB is widely used in display applications, including monitors, TVs, and mobile devices.

Conversion Process

Converting LVDS display output to RGB involves several steps:

Step 1: LVDS to TTL Conversion

The first step in converting LVDS to RGB is to convert the LVDS signal to a TTL (Transistor-Transistor Logic) signal. This can be done using an LVDS to TTL converter IC, such as the Texas Instruments SN65LVDS1.

Step 2: TTL to RGB Conversion

Once the LVDS signal is converted to TTL, it needs to be converted to RGB format. This can be done using a TTL to RGB converter IC, such as the Adafruit RGB LCD Shield.

Step 3: Display Driver IC

The final step in converting LVDS to RGB is to use a display driver IC, such as the ST7789, to drive the RGB display.

Designing a Custom Board

To design a custom board for converting LVDS display output to RGB, you will need to follow these steps:

Step 1: Choose a Microcontroller

Select a microcontroller that supports the AM625 SoC and has the necessary peripherals for LVDS to RGB conversion. Some popular options include the Texas Instruments TM4C123GH6PM and the STMicroelectronics STM32F407.

Step 2: Choose a Display Driver IC

Select a display driver IC that supports the RGB display and has the necessary features for driving the display. Some popular options include the ST7789 and the ILI9341.

Step 3: Design the Board Layout

Design the board layout using a CAD tool, such as Eagle or KiCad. Ensure that the board layout is compact and efficient, with minimal noise and interference.

Step 4: Implement the Conversion Logic

Implement the conversion logic using a programming language, such as C or Python. Use a library or framework that supports the microcontroller and display driver IC.

Example Code

Here is an example code for converting LVDS display output to RGB using the Texas Instruments TM4C123GH6PM microcontroller and the ST7789 display driver IC:

#include <stdint.h>
#include <stdbool.h>
#include <driverlib/gpio.h>
#include <driverlib/pin_map.h>
#include <driverlib/sysctl.h>
#include <driverlib/uart.h>
#include <driverlib/rom.h>
#include <driverlib/interrupt.h>
// Define the LVDS pins
#define LVDS_PIN_SDA  GPIO_PIN_0
#define LVDS_PIN_SCL  GPIO_PIN_1
// Define the RGB pins
#define RGB_PIN_RED  GPIO_PIN_2
#define RGB_PIN_GREEN  GPIO_PIN_3
#define RGB_PIN_BLUE  GPIO_PIN_4
// Define the display driver IC pins
#define DDC_PIN_SDA  GPIO_PIN_5
#define DDC_PIN_SCL  GPIO_PIN_6
// Define the display driver IC registers
#define DDC_REG_COMMAND  0x00
#define DDC_REG_DATA  0x01
// Define the display driver IC commands
#define DDC_CMD_SET_ADDRESS  0x00
#define DDC_CMD_SET_DATA  0x01
// Define the display driver IC data
#define DDC_DATA_SET_ADDRESS  0x00
#define DDC_DATA_SET_DATA  0x01
// Function to convert LVDS to TTL
void lvds_to_ttl(void) {
// Set the LVDS pins as outputs
GPIO_setConfig(LVDS_PIN_SDA, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
GPIO_setConfig(LVDS_PIN_SCL, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
// Set the LVDS pins high
GPIO_setOutputHighOnPin(LVDS_PIN_SDA);
GPIO_setOutputHighOnPin(LVDS_PIN_SCL);
}
// Function to convert TTL to RGB
void ttl_to_rgb(void) {
// Set the RGB pins as outputs
GPIO_setConfig(RGB_PIN_RED, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
GPIO_setConfig(RGB_PIN_GREEN, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
GPIO_setConfig(RGB_PIN_BLUE, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
// Set the RGB pins high
GPIO_setOutputHighOnPin(RGB_PIN_RED);
GPIO_setOutputHighOnPin(RGB_PIN_GREEN);
GPIO_setOutputHighOnPin(RGB_PIN_BLUE);
}
// Function to convert RGB to display driver IC
void rgb_to_ddc(void) {
// Set the display driver IC pins as outputs
GPIO_setConfig(DDC_PIN_SDA, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
GPIO_setConfig(DDC_PIN_SCL, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
// Set the display driver IC pins high
GPIO_setOutputHighOnPin(DDC_PIN_SDA);
GPIO_setOutputHighOnPin(DDC_PIN_SCL);
}
// Function to drive the display
void drive_display(void) {
// Convert LVDS to TTL
lvds_to_ttl();
// Convert TTL to RGB
ttl_to_rgb();
// Convert RGB to display driver IC
rgb_to_ddc();
// Set the display driver IC command
GPIO_setOutputLowOnPin(DDC_PIN_SDA);
GPIO_setOutputLowOnPin(DDC_PIN_SCL);
GPIO_setOutputHighOnPin(DDC_PIN_SDA);
GPIO_setOutputHighOnPin(DDC_PIN_SCL);
// Set the display driver IC data
GPIO_setOutputLowOnPin(DDC_PIN_SDA);
GPIO_setOutputLowOnPin(DDC_PIN_SCL);
GPIO_setOutputHighOnPin(DDC_PIN_SDA);
GPIO_setOutputHighOnPin(DDC_PIN_SCL);
// Drive the display
while (1) {
// Do nothing
}
}
int main(void) {
// Initialize the system
SysCtl_clockConfigure(SYSCTL_XTAL_16MHZ, SYSCTL_OSC_MAIN, SYSCTL_USE_PLL, 72000000);
// Initialize the GPIO pins
GPIO_setConfig(GPIO_PORTA_BASE, GPIO_CFG_OUT_STD | GPIO_CFG_OUT_STRONG);
// Drive the display
drive_display();
// Return 0
return 0;
}

Conclusion

Introduction

In our previous article, we discussed the process of converting LVDS display output to RGB for the AM625 SBC. However, we understand that there may be many questions and concerns that readers may have. In this article, we will address some of the most frequently asked questions and provide additional information to help you better understand the process.

Q: What is the difference between LVDS and RGB?

A: LVDS (Low-Voltage Differential Signaling) is a high-speed, low-voltage signaling technology used for transmitting digital data between devices. It uses a differential signaling scheme, where two complementary signals are transmitted over a single wire pair. RGB (Red, Green, Blue) is a color model used to represent colors on a display device. It uses three primary colors - red, green, and blue - to create a wide range of colors.

Q: Why do I need to convert LVDS to RGB?

A: If you have an LVDS display, you will need to convert the LVDS output to RGB format in order to drive the display. This is because most display driver ICs and microcontrollers support RGB output, but not LVDS output.

Q: What are the advantages of converting LVDS to RGB?

A: The advantages of converting LVDS to RGB include:

Improved display quality: Converting LVDS to RGB can improve the display quality by reducing noise and interference.
Increased flexibility: Converting LVDS to RGB allows you to use a wider range of display driver ICs and microcontrollers.
Simplified design: Converting LVDS to RGB can simplify the design process by reducing the number of components required.

Q: What are the challenges of converting LVDS to RGB?

A: The challenges of converting LVDS to RGB include:

Complexity: Converting LVDS to RGB can be a complex process, requiring a deep understanding of LVDS and RGB signaling technologies.
Noise and interference: Converting LVDS to RGB can introduce noise and interference, which can affect the display quality.
Component selection: Selecting the right components for converting LVDS to RGB can be challenging, requiring careful consideration of factors such as speed, accuracy, and power consumption.

Q: What are the common applications of converting LVDS to RGB?

A: The common applications of converting LVDS to RGB include:

Display drivers: Converting LVDS to RGB is commonly used in display drivers, such as LCD and OLED displays.
Microcontrollers: Converting LVDS to RGB is commonly used in microcontrollers, such as ARM and x86 processors.
Embedded systems: Converting LVDS to RGB is commonly used in embedded systems, such as robots and drones.

Q: What are the common tools and software used for converting LVDS to RGB?

A: The common tools and software used for converting LVDS to RGB include:

CAD tools: CAD tools, such as Eagle and KiCad, are commonly used for designing and simulating the conversion circuit.
Programming languages: Programming languages, such as C and Python, are commonly used for implementing the conversion logic.
Simulation software: Simulation software, such as SPICE and ModelSim, are commonly used for simulating the conversion circuit and verifying its performance.

Q: What are the common mistakes to avoid when converting LVDS to RGB?

A: The common mistakes to avoid when converting LVDS to RGB include:

Incorrect component selection: Selecting the wrong components can lead to poor performance and reliability issues.
Insufficient noise reduction: Failing to reduce noise and interference can lead to poor display quality and reliability issues.
Inadequate testing: Failing to thoroughly test the conversion circuit can lead to reliability issues and poor performance.

Conclusion

Converting LVDS display output to RGB for the AM625 SBC requires a deep understanding of the LVDS and RGB signaling technologies, as well as the display driver IC. By following the steps outlined in this article and avoiding common mistakes, you can design a custom board for converting LVDS display output to RGB and drive the display using a microcontroller and display driver IC.