STM32 Modbus Display

Short Description

This project implements a Modbus RTU slave for an STM32 microcontroller. It communicates with a Modbus master device over a UART interface and displays data on an SSD1306 OLED display. Key features include:

• Modbus RTU Communication: Initialization, enabling, and handling read/write operations on holding registers.
• OLED Display Control: Manages an SSD1306 OLED display, displaying text and graphics based on holding register values.
• User Interface: Provides a user interface with three keys (Up, Down, Enter) and a buzzer, controllable via holding registers.
• EEPROM Storage: Stores and retrieves configuration data (baud rate, Modbus ID) in EEPROM, modifiable through Modbus holding registers.
• Holding Register Management: Defines holding registers for storing display text, key states, buzzer control, and configuration settings.

Table of Contents

• Config Timer
• Config LCD
• Config EEPROM
• Key & Buzzer
• Display Initialization
• Main Loop
• Modbus Register Table
• Python GUI
• Roadmap

Config Timer

1. Select the Timer: Timer 3 (TIM3) is used for Modbus timing.
2. Configure the Timer Prescaler: Set to 71, resulting in a timer clock frequency of 1 MHz (assuming a system clock of 72 MHz).
3. Set the Timer Period: Set to 50, corresponding to an interrupt interval of 50 microseconds (50 μs).
4. Set the Timer Counter Mode: Set to TIM_COUNTERMODE_UP.
5. Initialize the Timer: Use HAL_TIM_Base_Init to initialize the timer.
6. Pass the Timer Handle to Modbus: Pass the configured timer handle (htim3) to ModbusRtuInit.

• Refer to freemodbus Porting Doc for more details about timing and microtechnics for porting the freemodbus to STM32.

Config LCD

1. Configure I2C: Set up I2C in STM32CubeMX for SSD1306 display communication.
2. Select Font Size: Choose a font size (e.g., Font_11x18) from the provided font files.
3. Set Holding Register Addresses: Set addresses and size based on font size and maximum characters.
4. Update Holding Registers: Update with the text to be displayed.
5. Refresh Display: Call ssd1306_UpdateScreen to refresh the OLED display.

Refer to ssd1306-stm32HAL for more details.

Config EEPROM

To store settings on the microcontroller, we use the EEPROM emulation library written by NimaLTD. The structure for storing information is defined in rtudisplay.h:

typedef struct {
  USHORT Baudrate;
  USHORT ModbusID;
} Storage_t;

Refer to EEPROM EMULATION Library for STM32 for more details.

Key & Buzzer

Provides a simple user interface with three keys (Up, Down, Enter) and a buzzer. Key states are stored in holding registers, and the buzzer is controlled via holding registers:

• Key States: Set corresponding holding register to 1 when a key is pressed.
• Buzzer Control: Write specific values to the holding register at Buzzer_ADDR to control the buzzer:
  • 1: buzzer_beep (short beep)
  • 2: BUZZER_ON (continuous on)
  • 3: BUZZER_OFF (off)

Display Initialization

The Rtudisplay_Init function initializes various components:

1. Initialize Holding Registers: Set HRBuff array to zeros.
2. Initialize EEPROM: Call EE_Init with EE_Setting structure.
3. Read EEPROM Settings: Call EE_Read.
4. Set Default Values if Invalid:

• Baud rate default: 3 (9600)
• Modbus ID default: 2

5. Copy Settings to Holding Registers:

• Baud_ADDR
• MbID_ADDR

6. Set Baud Rate: Based on EE_Setting.Baudrate.
7. Initialize UART: Call HAL_UART_Init with huart2.
8. Initialize Modbus: Call ModbusRtuInit.
9. Initialize OLED Display: Call ssd1306_Init with hi2c1.

Main Loop

The main program loop (while(1)) performs the following:

1. Handle Modbus Communication: Call eMBPoll().
2. Update Display and Save Parameters: If Write on Holding Register function received and HR_Write_Flag is set.
3. Update Buzzer State: Based on holding register.
4. Update Key States: Reflect in holding registers. This loop keeps the system responsive to Modbus, user input, and events requiring display or buzzer updates.

Mbus-Table

Address	Description
40001-----40011	LCD Line 1
40012-----40022	LCD Line 2
40023-----40033	LCD Line 3
40034-----40036	Reserved
40037	Modbus ID
40038	Baud Rate
40039	Save Settings
40040	Up Key
40041	Down Key
40042	Enter Key
40043	Buzzer

guipython

This project offers a GUI for interacting with Modbus Dispaly RTU via Tkinter in Python, allowing users to configure communication, control a buzzer, and monitor keys and LEDs. Access the software here.

roadmap

• The RS485 Directin Control pin declared at init function (Currently in Library\Modbus\rtu\mbrtu.c line 302,315 ) !!
• Support multi-size font for each line
• Add Changelog