How STM32 interacts with serial port screens?

STM32 microcontrollers can communicate with serial port display screens (also called UART TFT screens) using standard UART (USART) interfaces. These screens often include a built-in microcontroller and use a command-based protocol over a serial connection (TX/RX).

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1. Basic Hardware Connection

Voltage levels must match — if the screen is 5V and STM32 is 3.3V, use a level shifter.

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2. Communication Protocol

Most UART screens (e.g., Nextion, ST7920 UART modules, or custom ones) follow a command format like:

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Command bytes → [Header] + [Command ID] + [Data] + [Checksum/End bytes]

Or simply:

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"page 1\xff\xff\xff"  → Change to page 1 (Nextion example)

You send these via HAL_UART_Transmit(), e.g.:

c

char cmd[] = "page home\xff\xff\xff";
HAL_UART_Transmit(&huart1, (uint8_t*)cmd, strlen(cmd), HAL_MAX_DELAY);

Some screens also send responses back to STM32 (e.g., button presses).

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3. STM32 HAL UART Setup

In STM32CubeMX / STM32CubeIDE:

1. Enable USART1 (or any USART).

2. Set:

   • Baud Rate (e.g., 9600 or 115200)

   • 8 data bits, no parity, 1 stop bit (default)

3. Generate code.

4. Initialize the UART (HAL handles this in MX_USARTx_UART_Init()).

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4. Interfacing in Code

Transmitting Data (STM32 → Screen):

c

char txt[] = "t0.txt=\"Hello\"\xff\xff\xff";
HAL_UART_Transmit(&huart1, (uint8_t*)txt, strlen(txt), HAL_MAX_DELAY);

Receiving Data (Screen → STM32):

You can use:

• HAL_UART_Receive() (blocking)

• HAL_UART_Receive_IT() (interrupt)

• HAL_UART_Receive_DMA() (non-blocking, fast)

Example:

c

uint8_t rxData[10];
HAL_UART_Receive_IT(&huart1, rxData, sizeof(rxData));

In USARTx_IRQHandler(), handle parsing of response frames.

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5. Popular UART Display Modules

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Advantages of UART Screens

• No need to handle raw LCD commands

• Easy to interface: just send strings or frames

• Offloads rendering work to the display

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Common Pitfalls

• Wrong baud rate or voltage level mismatch

• Incomplete commands (missing end markers like \xff\xff\xff)

• Ignoring UART buffer overflows when receiving fast data

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Bonus: Debugging Tips

• Use a USB-to-Serial adapter and terminal (e.g., PuTTY) to test screen commands.

• Connect logic analyzer (e.g., Saleae) to monitor TX/RX signals.

• Add delays between commands if the screen is slow to respond.