72. Serial Communication

Learn how to send and receive data with external devices using serial communication.

72.1 Enumerating Serial Ports

• You can get a list of serial ports recognized by the PC with System::EnumerateSerialPorts()
• The result is returned as Array<SerialPortInfo> type
• The member variables of SerialPortInfo type are as follows:

Code	Description
String port	Serial port name
String description	Serial port description
String hardwareID	Hardware ID

# include <Siv3D.hpp>

void Main()
{
	for (const auto& info : System::EnumerateSerialPorts())
	{
		Print << U"[{}] {}"_fmt(info.port, info.description);
	}

	while (System::Update())
	{

	}
}

Output Example

[COM3] USB Serial Device (COM3)
[COM4] Arduino Uno (COM4)

72.2 Selecting COM Port to Connect

• You can create a GUI to select the serial port to connect using functions like the following

# include <Siv3D.hpp>

Array<String> GetSerialPortOptions(const Array<SerialPortInfo>& infos)
{
	Array<String> options = infos.map([](const SerialPortInfo& info)
	{
		return U"[{}] {}"_fmt(info.port, info.description);
	});

	options << U"None";
	return options;
}

void Main()
{
	const Array<SerialPortInfo> infos = System::EnumerateSerialPorts();
	const Array<String> options = GetSerialPortOptions(infos);
	size_t index = (options.size() - 1);

	while (System::Update())
	{
		if (SimpleGUI::RadioButtons(index, options, Vec2{ 200, 60 }))
		{

		}
	}
}

72.3 Serial Class Basics

• You can perform serial communication using the Serial class
• Main features of the Serial class:
  • Connect to and disconnect from serial ports
  • Send and receive data (byte units, binary data)
  • Buffer management and clearing
  • Check connection status
  • Control handshake signals (RTS, DTR)
  • Get line signal status (CTS, DSR, RI, CD)
• Read operations:
  • Read byte data
  • Read into arrays
  • Read into trivially copyable types
• Write operations:
  • Write byte data
  • Write binary data
  • Write trivially copyable types
• In the constructor, you can set detailed options as needed:
  • ByteSize (5-8 bits)
  • Parity (None, Odd, Even, Mark, Space)
  • StopBits (One, Two, OnePointFive)
  • FlowControl (None, Software, Hardware)

72.4 Serial Communication (1 Byte)

• This is a sample of bidirectional communication where the LED on Arduino is controlled from the PC side, while simultaneously sending data from Arduino to the PC side

Troubleshooting Communication Issues

• If serial communication is unstable, opening and then closing the serial monitor in Arduino IDE may improve the situation

Arduino Side Code

• Runs on the Arduino board and handles communication with PC and LED control
• Initial Setup (setup function):
  • Set pin 13 to output mode (to control LED)
  • Start serial communication at 9600 bps baud rate
• Main Loop (loop function):
  • Operates every 250 milliseconds
  • Send value of variable i to PC, then increment it
  • Receive and process data sent from PC side:
    • Receive 0: Turn LED off (LOW)
    • Receive 1: Turn LED on (HIGH)
    • Receive 2: Reset counter i
  • If no data is received, do nothing and proceed to next loop

void setup()
{
	// Set pin 13 to output mode
	pinMode(13, OUTPUT);

	// Open serial port at 9600 bps
	Serial.begin(9600);
}

uint8_t i = 0; // Value to send to PC (1 byte)

void loop()
{
	// Wait 250 milliseconds
	delay(250);

	// Output 1 byte to serial port
	Serial.write(i);

	++i;

	if (0 < Serial.available())
	{
		// Read data received via serial communication
		const int val = Serial.read();

		if (val == 0)
		{
			// Turn LED off
			digitalWrite(13, LOW);
		}
		else if (val == 1)
		{
			// Turn LED on
			digitalWrite(13, HIGH);
		}
		else if (val == 2)
		{
			// Reset counter
			i = 0;
		}
	}
}

PC Side Code

• Communication with Arduino and GUI program
• Main Processing:
  • "Write 0" button: Send 0 to Arduino (turn LED off)
  • "Write 1" button: Send 1 to Arduino (turn LED on)
  • "Write 2" button: Send 2 to Arduino (reset counter)
  • Display data received from Arduino on screen

# include <Siv3D.hpp>

Array<String> GetSerialPortOptions(const Array<SerialPortInfo>& infos)
{
	Array<String> options = infos.map([](const SerialPortInfo& info)
	{
		return U"[{}] {}"_fmt(info.port, info.description);
	});

	options << U"None";
	return options;
}

void Main()
{
	const Array<SerialPortInfo> infos = System::EnumerateSerialPorts();
	const Array<String> options = GetSerialPortOptions(infos);
	size_t index = (options.size() - 1);
	Serial serial;

	while (System::Update())
	{
		const bool isOpen = serial.isOpen();

		if (SimpleGUI::Button(U"Write 0", Vec2{ 200, 20 }, 120, isOpen))
		{
			// Write 1 byte of data (0)
			serial.writeByte(0);
		}

		if (SimpleGUI::Button(U"Write 1", Vec2{ 340, 20 }, 120, isOpen))
		{
			// Write 1 byte of data (1)
			serial.writeByte(1);
		}

		if (SimpleGUI::Button(U"Write 2", Vec2{ 480, 20 }, 120, isOpen))
		{
			// Write 1 byte of data (2)
			serial.writeByte(2);
		}

		if (SimpleGUI::RadioButtons(index, options, Vec2{ 200, 60 }))
		{
			ClearPrint();

			if (index == (options.size() - 1))
			{
				// Close serial port
				serial = Serial{};
			}
			else
			{
				Print << U"Open {}"_fmt(infos[index].port);

				// Open serial port
				if (serial.open(infos[index].port))
				{
					Print << U"Succeeded";
				}
				else
				{
					Print << U"Failed";
				}
			}
		}

		if (const size_t available = serial.available())
		{
			// Read and display data received via serial communication
			Print << U"READ: " << serial.readBytes();
		}
	}
}

72.5 Serial Communication (Multiple Bytes)

• This is a sample for multi-byte communication
• The PC side sends a 16-bit integer, which Arduino receives, adds 1 to, and sends back

Arduino Side Code

void setup()
{
	Serial.begin(9600);
}

void loop()
{
	delay(250);

	if (2 <= Serial.available())
	{
    	// Read 2 bytes of data
		int low = Serial.read();
		int high = Serial.read();
		
		// Convert to 16-bit integer and add 1
		uint16_t n = (high << 8) | low;
		n += 1;

		// Send result
		Serial.write(lowByte(n));
		Serial.write(highByte(n));
	}
}

PC Side Code

# include <Siv3D.hpp>

Array<String> GetSerialPortOptions(const Array<SerialPortInfo>& infos)
{
	Array<String> options = infos.map([](const SerialPortInfo& info)
	{
		return U"[{}] {}"_fmt(info.port, info.description);
	});

	options << U"None";
	return options;
}

void Main()
{
	const Array<SerialPortInfo> infos = System::EnumerateSerialPorts();
	const Array<String> options = GetSerialPortOptions(infos);
	size_t index = (options.size() - 1);
	Serial serial;

	while (System::Update())
	{
		const bool isOpen = serial.isOpen();

		if (SimpleGUI::Button(U"Write uint16", Vec2{ 200, 20 }, 160, isOpen))
		{
			// Write 2 bytes (uint16) of data
			const uint16 n = 12300;
			serial.write(n);
		}

		if (SimpleGUI::RadioButtons(index, options, Vec2{ 200, 60 }))
		{
			ClearPrint();

			if (index == (options.size() - 1))
			{
				// Close serial port
				serial = Serial{};
			}
			else
			{
				Print << U"Open {}"_fmt(infos[index].port);

				// Open serial port
				if (serial.open(infos[index].port))
				{
					Print << U"Succeeded";
				}
				else
				{
					Print << U"Failed";
				}
			}
		}

		if (const size_t available = serial.available();
			2 <= available)
		{
			// Read and display 2 bytes of data
			uint16 n;
			if (serial.read(n))
			{
				Print << U"READ: " << n;
			}
		}
	}
}

72.6 Serial Communication (String)

• This is a sample that modifies 72.5 to send strings from Arduino

Arduino Side Code

void setup()
{
	Serial.begin(9600);
}

void loop()
{
	delay(250);

	if (2 <= Serial.available())
	{
    	// Read 2 bytes of data
		int low = Serial.read();
		int high = Serial.read();
		
		// Convert to 16-bit integer and add 1
		uint16_t n = (high << 8) | low;
		n += 1;

		// Send result as string
		Serial.print("The answer is ");
		Serial.println(n);
	}
}

PC Side Code

# include <Siv3D.hpp>

Array<String> GetSerialPortOptions(const Array<SerialPortInfo>& infos)
{
	Array<String> options = infos.map([](const SerialPortInfo& info)
	{
		return U"[{}] {}"_fmt(info.port, info.description);
	});

	options << U"None";
	return options;
}

void Main()
{
	const Array<SerialPortInfo> infos = System::EnumerateSerialPorts();
	const Array<String> options = GetSerialPortOptions(infos);
	size_t index = (options.size() - 1);
	Serial serial;

	std::string buffer;

	while (System::Update())
	{
		const bool isOpen = serial.isOpen();

		if (SimpleGUI::Button(U"Write uint16", Vec2{ 200, 20 }, 160, isOpen))
		{
			// Write 2 bytes (uint16) of data
			const uint16 n = 12300;
			serial.write(n);
		}

		if (SimpleGUI::RadioButtons(index, options, Vec2{ 200, 60 }))
		{
			ClearPrint();

			if (index == (options.size() - 1))
			{
				// Close serial port
				serial = Serial{};
			}
			else
			{
				Print << U"Open {}"_fmt(infos[index].port);

				// Open serial port
				if (serial.open(infos[index].port))
				{
					Print << U"Succeeded";
				}
				else
				{
					Print << U"Failed";
				}
			}
		}

		if (const size_t available = serial.available())
		{
			const Array<uint8> bytes = serial.readBytes();

			for (const auto& ch : bytes)
			{
				if (ch == '\r') // Ignore CR
				{
					continue;
				}
				else if (ch == '\n') // End of line
				{
					// Display the string read for one line
					Print << Unicode::FromUTF8(buffer);
					buffer.clear();
				}
				else
				{
					buffer.push_back(ch);
				}
			}
		}
	}
}