Technical White Paper: Driving 7 inch TFT LCD with STM32 MCU
1 Overview
This paper details the implementation of a display driver system using an STM32H7 microcontroller to directly drive the LMT070ENMFWA-NND-2 7-inch TFT LCD via the LTDC interface. The system includes display initialization, LTDC configuration, backlight control, clock synchronization, and touch panel interfacing.
2 Hardware Overview
Microcontroller: STM32H743ZI (or any STM32H7 with LTDC and enough memory bandwidth)
Display: LMT070ENMFWA-NND-2 TFT LCD (800x480, RGB888 interface)
Touch Panel: Capacitive touch with I2C interface
External RAM: SDRAM (for framebuffer)
2.1 STM32H743ZI MCU
The STM32H743ZI is a high-performance MCU based on the ARM Cortex-M7 core. It features high clock speeds, substantial on-chip memory, and a wide range of peripherals, making it suitable for demanding embedded applications. Key features include:
- High-performance ARM Cortex-M7 core
- Clock frequency up to 480 MHz
- Integrated LCD controller
- Extensive memory resources
- High-speed communication interfaces
2.2 LMT070ENMFWA-NND-2 TFT LCD
The TOPWAY LMT070ENMFWA-NND-2 is a 7-inch TFT LCD module designed for applications requiring high-quality flat panel displays. It features a capacitive touch panel and is composed of an IPS TFT-LCD panel, driver ICs, FPC, and an LED backlight unit.
- Display Technology: a-Si IPS TFT active matrix
- Resolution: 1024 x 3(RGB) x 600
- Interface: Digital 24-bit RGB
- Backlight: White LED
- Capacitive Touch Panel: ILI2511 driver IC
3 Hardware Interface and Configuration
3.1 TFT LCD Interface
The LMT070ENMFWA-NND-2 module uses a 24-bit RGB digital interface for data input. The interface includes signals for data, synchronization, and control.
Data Signals: R0-R7, G0-G7, B0-B7 (8-bit data for each color)
Synchronization Signals: HS (Horizontal Sync Input), VS (Vertical Sync Input), DE (Data Input Enable)
Clock Signal: DCLK (Sample Clock)
Control Signals: MODE (DE/SYNC mode select), L/R (Left/right selection), U/D (Up/down selection), DITHB (Dithering setting), RESET (Global reset pin)
3.2 Capacitive Touch Panel Interface
The module integrates a capacitive touch panel, which communicates via the I2C interface.
I2C Signals: SDA (I2C Data), SCL (I2C Clock)
Other Signals: RST (Touch Panel Reset), INT (Touch Panel INT)
3.3 STM32H743ZI Configuration
The STM32H743ZI MCU provides an LCD controller that can be configured to interface with the TFT LCD. The configuration involves setting up the timing parameters, data format, and other control signals to match the requirements of the LMT070ENMFWA-NND-2 module.
LCD Controller Configuration:
Setting the horizontal and vertical timing parameters
Configuring the pixel clock and data format
Enabling the required layers and interrupts
GPIO Configuration:
Configuring the GPIO pins for the RGB data signals
Setting up GPIOs for the control and synchronization signals (HS, VS, DE, MODE, etc.)
Initializing GPIOs for the I2C interface (SDA, SCL) for touch panel communication
I2C Configuration:
Initializing the I2C peripheral for communication with the capacitive touch panel
Setting the clock frequency and addressing mode
3.4 Hardware Connection
| STM32H7 Pin | LCD Pin | Function | Notes |
|---|---|---|---|
| LTDC_R[0..7] | R0-R7 | Red color bits | RGB888 |
| LTDC_G[0..7] | G0-G7 | Green color bits | |
| LTDC_B[0..7] | B0-B7 | Blue color bits | |
| LTDC_CLK | DCLK | Pixel clock | ~33-50MHz |
| LTDC_HSYNC | HSYNC | Horizontal sync | |
| LTDC_VSYNC | VSYNC | Vertical sync | |
| LTDC_DE | DE | Data enable | |
| VDD (3.3V) | VDD | Power | |
| GND | GND | Ground | |
| TIMx_CHx (PWM Out) | VLED+ | Backlight control (PWM) | |
| GPIO (Open drain) | VLED- | Backlight GND | |
| I2C1_SCL | TP_SCL | Touch Panel I2C Clock | |
| I2C1_SDA | TP_SDA | Touch Panel I2C Data | |
| GPIO_EXTI | TP_INT | Touch Panel Interrupt |
Optional |
4. Implementation
4.1 Initialization Sequence
Below is an example that covers the key parts of the initialization process for the STM32H7 using the HAL library. (Many functions are usually generated by STM32CubeMX; here, we illustrate the core custom code sections.)
Power Sequence:
- Digital/Analog Supply: Apply DVDD (3.3V) and AVDD (if used).
- Gate Driver Voltages: Apply VGL first, then VGH.
- Backlight: Apply VLED+ (with current limiting) and VLED– after core voltages are stable.
Initialization Steps:
- HAL and System Clock (with PLL3 for LTDC)
- LTDC initialization with timing parameters set for 1024×600 resolution
- FMC (SDRAM) initialization for the framebuffer
- I2C initialization for the capacitive touch panel
- Timer (PWM) initialization for backlight control
4.2 Code Examples
4.2.1 HAL Initialization and System Clock Configuration
#include "stm32h7xx_hal.h"
/* System Clock Configuration
This configuration uses PLLs to generate the system clock as well as the LTDC pixel clock.
Adjust PLL3 parameters as needed for your target pixel clock (for example, ~33-50MHz for DCLK).
*/
void SystemClock_Config(void)
{
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};
// Enable HSE Oscillator and activate PLL with HSE as source
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_ON;
RCC_OscInitStruct.HSIState = RCC_HSI_OFF;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
// Configure PLL1 for system clock (example values, adjust per your board)
RCC_OscInitStruct.PLL.PLLM = 5;
RCC_OscInitStruct.PLL.PLLN = 240;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLR = 2;
if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
{
// Initialization Error
while(1);
}
// Select PLL1 as system clock source and configure bus clocks dividers
RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK |
RCC_CLOCKTYPE_D1PCLK1 | RCC_CLOCKTYPE_D3PCLK1;
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4) != HAL_OK)
{
// Initialization Error
while(1);
}
// LTDC Clock: Configure PLL3 to generate the pixel clock for LTDC
PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_LTDC;
// Example: Adjust PLL3 parameters (these numbers are placeholders – set them for your pixel clock)
PeriphClkInitStruct.PLL3.PLL3M = 5;
PeriphClkInitStruct.PLL3.PLL3N = 132;
PeriphClkInitStruct.PLL3.PLL3R = 2; // Resulting in: ((HSE/PLL3M)*PLL3N)/PLL3R ~ desired DCLK frequency
if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
{
while(1);
}
}
4.2.2 LTDC Initialization
The LTDC peripheral drives the LCD. This snippet configures the timing parameters, background color, and one layer (assuming single-layer configuration):
#include "stm32h7xx_hal_ltdc.h"
LTDC_HandleTypeDef hltdc;
void MX_LTDC_Init(void)
{
LTDC_LayerCfgTypeDef pLayerCfg = {0};
hltdc.Instance = LTDC;
hltdc.Init.HSPolarity = LTDC_HSPOLARITY_AL;
hltdc.Init.VSPolarity = LTDC_VSPOLARITY_AL;
hltdc.Init.DEPolarity = LTDC_DEPOLARITY_AL;
hltdc.Init.PCPolarity = LTDC_PCPOLARITY_IPC;
// Timing parameters based on LCD datasheet (adjust these for your display)
hltdc.Init.HorizontalSync = 40;
hltdc.Init.VerticalSync = 9;
hltdc.Init.AccumulatedHBP = 88;
hltdc.Init.AccumulatedVBP = 32;
hltdc.Init.AccumulatedActiveW = 888;
hltdc.Init.AccumulatedActiveH = 512;
hltdc.Init.TotalWidth = 928;
hltdc.Init.TotalHeigh = 525;
hltdc.Init.Backcolor.Blue = 0;
hltdc.Init.Backcolor.Green = 0;
hltdc.Init.Backcolor.Red = 0;
if(HAL_LTDC_Init(&hltdc) != HAL_OK)
{
while(1);
}
// Configure Layer 0 for the display
pLayerCfg.WindowX0 = 0;
pLayerCfg.WindowX1 = 1024;
pLayerCfg.WindowY0 = 0;
pLayerCfg.WindowY1 = 600;
pLayerCfg.PixelFormat = LTDC_PIXEL_FORMAT_RGB888;
// FRAMEBUFFER_ADDR should point to the external SDRAM where the frame is stored
pLayerCfg.FBStartAdress = FRAMEBUFFER_ADDR;
pLayerCfg.Alpha = 255;
pLayerCfg.Alpha0 = 0;
pLayerCfg.BlendingFactor1 = LTDC_BLENDING_FACTOR1_CA;
pLayerCfg.BlendingFactor2 = LTDC_BLENDING_FACTOR2_CA;
pLayerCfg.ImageWidth = 1024;
pLayerCfg.ImageHeight = 600;
if(HAL_LTDC_ConfigLayer(&hltdc, &pLayerCfg, 0) != HAL_OK)
{
while(1);
}
}
4.2.3 I2C Initialization
The touch panel communicates over I2C. Again, CubeMX can generate the basic configuration, but here’s a sample:
I2C_HandleTypeDef hi2c1;
void MX_I2C1_Init(void)
{
hi2c1.Instance = I2C1;
hi2c1.Init.Timing = 0x40912732; // Example timing value, adjust per your system clock and desired I2C speed.
hi2c1.Init.OwnAddress1 = 0;
hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
hi2c1.Init.OwnAddress2 = 0;
hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
if (HAL_I2C_Init(&hi2c1) != HAL_OK)
{
while(1);
}
}
4.2.4 Backlight Control Using PWM
We use a timer (e.g., TIMx) to generate a PWM signal that controls the backlight brightness. Configure the timer and its channel accordingly:
TIM_HandleTypeDef htimx;
void MX_TIMx_Init(void)
{
// Enable timer clock, configuration depends on the chosen timer (e.g., TIM3)
htimx.Instance = TIM3;
htimx.Init.Prescaler = 0; // Adjust as needed to get desired PWM frequency (e.g., 1kHz)
htimx.Init.CounterMode = TIM_COUNTERMODE_UP;
htimx.Init.Period = 1000 - 1; // For 1kHz PWM, adjust period to set resolution
htimx.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
if (HAL_TIM_PWM_Init(&htimx) != HAL_OK)
{
while(1);
}
TIM_OC_InitTypeDef sConfigOC = {0};
sConfigOC.OCMode = TIM_OCMODE_PWM1;
sConfigOC.Pulse = 500; // 50% duty cycle initial value
sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
if (HAL_TIM_PWM_ConfigChannel(&htimx, &sConfigOC, TIM_CHANNEL_1) != HAL_OK)
{
while(1);
}
}
void Set_Backlight(uint8_t brightness)
{
// brightness: value from 0 to (Period) i.e. 0 to 999 in this example.
__HAL_TIM_SET_COMPARE(&htimx, TIM_CHANNEL_1, brightness);
}
4.2.5 SDRAM (FMC) Initialization
The external SDRAM is used as the framebuffer. (CubeMX typically generates this code.) Here’s a simplified placeholder:
void MX_FMC_Init(void)
{
// FMC SDRAM initialization code – typically generated by CubeMX.
// Ensure that SDRAM timing parameters match your SDRAM chip.
// FRAMEBUFFER_ADDR must be defined in your linker script to point to SDRAM.
// ...
}
4.2.6 Main Loop
Update display framebuffer, poll touch inputs, and adjust backlight.
int main(void)
{
// 1. Initialize the HAL library
HAL_Init();
// 2. Configure the system clock
SystemClock_Config();
// 3. Initialize all configured peripherals
MX_FMC_Init(); // Initialize external SDRAM for the framebuffer
MX_LTDC_Init(); // Initialize the LTDC for the TFT
MX_I2C1_Init(); // Initialize I2C for the touch panel
MX_TIMx_Init(); // Initialize timer for PWM backlight control
HAL_TIM_PWM_Start(&htimx, TIM_CHANNEL_1); // Start PWM for backlight
// 4. Power sequence should be ensured by the hardware design:
// - Apply DVDD and AVDD, then VGL, then VGH, and finally enable backlight supply.
// This is managed externally and should be verified with proper delay circuits.
// 5. Initialize touchscreen if required (send any initialization commands via I2C)
// e.g., Touch_Init(); (implementation depends on your touch controller)
// 6. Main loop
while (1)
{
// Update framebuffer if necessary,
// Poll touch panel via I2C,
// Adjust backlight with Set_Backlight(brightness_value),
// Optionally use DMA2D for image processing.
}
}
5 Conclusion
This white paper has provided an overview of driving the TOPWAY LMT070ENMFWA-NND-2 TFT LCD module with the STM32H743ZI MCU. By carefully configuring the hardware and implementing the software according to the guidelines provided, developers can create robust and efficient graphical applications. The STM32H743ZI's powerful features and the LCD module's high-quality display make this combination suitable for a wide range of applications requiring a rich user interface.
Drop us an email, if you have embedded application project in-mind.