1. 定义LPT打印类
public class PrintFactory
{
public const short FILE_ATTRIBUTE_NORMAL = 0x80;
public const short INVALID_HANDLE_VALUE = -1;
public const uint GENERIC_READ = 0x80000000;
public const uint GENERIC_WRITE = 0x40000000;
public const uint CREATE_NEW = 1;
public const uint CREATE_ALWAYS = 2;
public const uint OPEN_EXISTING = 3;

[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr CreateFile(string lpFileName, uint dwDesiredAccess,
uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition,
uint dwFlagsAndAttributes, IntPtr hTemplateFile);

public static void SendCMDToLPT1( String receiptText )
{
IntPtr ptr = CreateFile("LPT1", GENERIC_WRITE, 0,
IntPtr.Zero, OPEN_EXISTING, 0, IntPtr.Zero);

if (ptr.ToInt32() == -1)
{
Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
}
else
{
FileStream lpt = new FileStream(ptr, FileAccess.ReadWrite);
Byte[] buffer = System.Text.Encoding.Default.GetBytes(receiptText);
lpt.Write(buffer, 0, buffer.Length);
lpt.Close();
}
}
}

2. 调用
PrintFactory.SendCMDToLPT1("ECS指令");