// ------------------------------------------------------------------------
// Create modbus header for write action
private byte[] CreateWriteHeader(ushort id, byte unit, ushort startAddress, ushort numData, ushort numBytes, EnumModbusFunctionCode function)
{
byte[] data = new byte[numBytes + 11];
byte[] _id = BitConverter.GetBytes((short)id);
data[0] = _id[1]; // Slave id high byte
data[1] = _id[0]; // Slave id low byte
byte[] _size = BitConverter.GetBytes((short)IPAddress.HostToNetworkOrder((short)(5 + numBytes)));
data[4] = _size[0]; // Complete message size in bytes
data[5] = _size[1]; // Complete message size in bytes
data[6] = unit; // Slave address
data[7] = (byte)function; // Function code
byte[] _adr = BitConverter.GetBytes((short)IPAddress.HostToNetworkOrder((short)startAddress));
data[8] = _adr[0]; // Start address
data[9] = _adr[1]; // Start address
if (function >= EnumModbusFunctionCode.WriteMultipleCoils)
{
byte[] _cnt = BitConverter.GetBytes((short)IPAddress.HostToNetworkOrder((short)numData));
data[10] = _cnt[0]; // Number of bytes
data[11] = _cnt[1]; // Number of bytes
data[12] = (byte)(numBytes - 2);
}
return(data);
}
// ------------------------------------------------------------------------
// Create modbus header for read action
private byte[] CreateReadHeader(ushort id, byte unit, ushort startAddress, ushort length, EnumModbusFunctionCode function)
{
byte[] data = new byte[12];
byte[] _id = BitConverter.GetBytes((short)id);
data[0] = _id[1]; // Slave id high byte
data[1] = _id[0]; // Slave id low byte
data[5] = 6; // Message size
data[6] = unit; // Slave address
data[7] = (byte)function; // Function code
byte[] _adr = BitConverter.GetBytes((short)IPAddress.HostToNetworkOrder((short)startAddress));
data[8] = _adr[0]; // Start address
data[9] = _adr[1]; // Start address
byte[] _length = BitConverter.GetBytes((short)IPAddress.HostToNetworkOrder((short)length));
data[10] = _length[0]; // Number of data to read
data[11] = _length[1]; // Number of data to read
return(data);
}
