test.c

#include <windows.h>
#include <stdio.h>

void setCommand(char* p, char s) {
	// three-byte format: 11111110 - 00AAAAAA - ACCDDDDD
	// if the engine is addressed with 23 (in binary: 10111), then AAAAAAA will be 0010111

	// the first byte is OFE
	*p |= 1 << 1;
	*p |= 1 << 2;
	*p |= 1 << 3;
	*p |= 1 << 4;
	*p |= 1 << 5;
	*p |= 1 << 6;
	*p |= 1 << 7;

	// the second byte: 00AAAAAA
	//engine addressing code:   000010111
	*(p + 1) |= 1 ;
	*(p + 1) |= 1 << 1;
	*(p + 1) |= 1 << 3;

	// the third byte: 1CCDDDDD
	*(p + 2) |= 1 << 7;

	switch (s) {
		// remain part for the third byte
	case 'h': // h - horn 1:   0011100
		*(p + 2) |= 1 << 2;
		*(p + 2) |= 1 << 3;
		*(p + 2) |= 1 << 4;
		break;

	default: break;
	}

}

int main()
{
    // Each command is in a three-byte command
	char bytes_to_send[3];
	bytes_to_send[0] = 0;
	bytes_to_send[1] = 0;
	bytes_to_send[2] = 0;

	setCommand(bytes_to_send, 'h');

	// Declare variables and structures
	HANDLE hSerial;
	DCB dcbSerialParams = { 0 };
	COMMTIMEOUTS timeouts = { 0 };

	// Open the right serial port number, normally on this computer should be COM1
	fprintf(stderr, "Opening serial port...");

	hSerial = CreateFile(
		"\\\\.\\COM1", GENERIC_READ | GENERIC_WRITE, 0, NULL,
		OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

	if (hSerial == INVALID_HANDLE_VALUE)
	{
		fprintf(stderr, "Error\n");
		return 1;
	}
	else fprintf(stderr, "OK\n");


	// Set device parameters (9600 baud, 1 start bit,
	// 1 stop bit, no parity)
	dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
	if (GetCommState(hSerial, &dcbSerialParams) == 0)
	{
		fprintf(stderr, "Error getting device state\n");
		CloseHandle(hSerial);
		return 1;
	}

	dcbSerialParams.BaudRate = CBR_9600;
	dcbSerialParams.ByteSize = 8;
	dcbSerialParams.StopBits = ONESTOPBIT;
	dcbSerialParams.Parity = NOPARITY;
	if (SetCommState(hSerial, &dcbSerialParams) == 0)
	{
		fprintf(stderr, "Error setting device parameters\n");
		CloseHandle(hSerial);
		return 1;
	}

	// Set COM port timeout settings
	timeouts.ReadIntervalTimeout = 50;
	timeouts.ReadTotalTimeoutConstant = 50;
	timeouts.ReadTotalTimeoutMultiplier = 10;
	timeouts.WriteTotalTimeoutConstant = 50;
	timeouts.WriteTotalTimeoutMultiplier = 10;
	if (SetCommTimeouts(hSerial, &timeouts) == 0)
	{
		fprintf(stderr, "Error setting timeouts\n");
		CloseHandle(hSerial);
		return 1;
	}

	// Send specified text (remaining command line arguments)
	DWORD bytes_written, total_bytes_written = 0;
	fprintf(stderr, "Sending bytes...");
	if (!WriteFile(hSerial, bytes_to_send, 3, &bytes_written, NULL))
	{
		fprintf(stderr, "Error\n");
		CloseHandle(hSerial);
		return 1;
	}
	fprintf(stderr, "%d bytes written\n", bytes_written);

    // Close serial port
	fprintf(stderr, "Closing serial port...");
	if (CloseHandle(hSerial) == 0)
	{
		fprintf(stderr, "Error\n");
		return 1;
	}
	fprintf(stderr, "OK\n");

	// exit normally

	return 0;
}

// reference: https://batchloaf.wordpress.com/2013/02/13/writing-bytes-to-a-serial-port-in-c/