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

void main ()
{
  // CreateFile
  HANDLE rs232 = CreateFileA ("\\.\COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
  if (rs232 == INVALID_HANDLE_VALUE)
  {
    printf ("fail CreateFile: %dn", GetLastError ()); system ("pause"); return;
  }

  // Get & Set CommState
  DCB port_configuration;
  int err = GetCommState (rs232, &port_configuration);
  if (err <= 0)
  {
    printf ("fail GetCommState: %dn", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
  }
  port_configuration.BaudRate = 19200;
  port_configuration.ByteSize = 8;
  port_configuration.Parity = 0;
  port_configuration.StopBits = 0;
  port_configuration.DCBlength = sizeof (port_configuration);
  err = SetCommState (rs232, &port_configuration);
  if (err <= 0)
  {
    printf ("fail SetCommStaten"); CloseHandle (rs232); system ("pause"); return;
  }

  // SetCommTimeouts
  COMMTIMEOUTS timeout_configuration;
  timeout_configuration.ReadIntervalTimeout = 1;// MAXDWORD;
  timeout_configuration.ReadTotalTimeoutMultiplier = 1;// 0;
  timeout_configuration.ReadTotalTimeoutConstant = 1;// 0;
  timeout_configuration.WriteTotalTimeoutMultiplier = 1;// 0;
  timeout_configuration.WriteTotalTimeoutConstant = 1;// 0;
  err = SetCommTimeouts (rs232, &timeout_configuration);
  if (err <= 0)
  {
    printf ("fail SetCommTimeouts: %dn", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
  }

  // WriteFile
  DWORD buffer_size_w;
  char buffer_w[128] = "*IDN?n";
  err = WriteFile (rs232, buffer_w, strlen (buffer_w), &buffer_size_w, 0);
  if (err <= 0)
  {
    printf ("fail WriteFile: %dn", GetLastError ()); CloseHandle (rs232); system ("pause"); return;
  }
  printf ("written %d characters: %sn", buffer_size_w, buffer_w);

  // ReadFile
  for (int x = 0; x < 10; ++x)
  {
    DWORD buffer_size_r;
    char buffer_r[128] = {0};
    err = ReadFile (rs232, buffer_r, 128, &buffer_size_r, 0);
    if (err <= 0)
    {
      printf ("fail ReadFile: %dn", GetLastError ()); Sleep (250); continue;
    }
    printf ("read %d characters: %sn", buffer_size_r, buffer_r);
    Sleep (250);
  }

  CloseHandle (rs232);
  system ("pause");
}