/// <summary>
/// Create modbus header for reading.
/// </summary>
/// <param name="myInvocationId"></param>
/// <param name="myStartAddress"></param>
/// <param name="myLength"></param>
/// <param name="myFunctionCode"></param>
/// <returns></returns>
public static MemoryStream CreateReadHeader(UInt16 myInvocationId, UInt16 myStartAddress, UInt16 myLength, FunctionCode myFunctionCode)
{
var _Header = CreateGenericHeader(myInvocationId, 6, myFunctionCode);
// Start address
var _adr = BitConverter.GetBytes((Int16)IPAddress.HostToNetworkOrder((Int16)myStartAddress));
_Header.WriteByte(_adr[0]); // high byte
_Header.WriteByte(_adr[1]); // low byte
// Number of data to read
var _length = BitConverter.GetBytes((Int16)IPAddress.HostToNetworkOrder((Int16)myLength));
_Header.WriteByte(_length[0]); // high byte
_Header.WriteByte(_length[1]); // low byte
return(_Header);
}
// Create modbus header for write action
public static MemoryStream CreateWriteHeader(UInt16 myInvocationId, UInt16 startAddress, UInt16 numData, Byte numBytes, FunctionCode myFunctionCode)
{
var _Header = CreateGenericHeader(myInvocationId, (UInt16)(numBytes + 5), myFunctionCode);
_Header.WriteWord(startAddress, ByteOrder.HostToNetwork);
if (myFunctionCode >= FunctionCode.WriteMultipleCoils)
{
_Header.WriteWord(numData, ByteOrder.HostToNetwork);
_Header.WriteByte((Byte)(numBytes - 2));
}
return(_Header);
}
public static MemoryStream CreateGenericHeader(UInt16 myInvocationId, UInt16 myMessageSize, FunctionCode myFunctionCode)
{
var _MemoryStream = new MemoryStream(20);
_MemoryStream.WriteWord(myInvocationId); // Invocation/Transaction Identifier
_MemoryStream.WriteWord(0); // Protocol Identifier (Zero for Modbus/TCP)
_MemoryStream.WriteWord(myMessageSize, ByteOrder.HostToNetwork); // Length Field/Message size
_MemoryStream.WriteByte(0); // Unit Identifier/Slave address (255 if not used)
_MemoryStream.WriteByte(myFunctionCode.Value); // Function code
return(_MemoryStream);
}
