Faced a problem. There is a 0x03 function, but I need to redo it in 0x06, I don’t understand how to do it.
I know that function 06 does not have a variable part. The value of one register is always transferred to it. But I can not understand what needs to be corrected. Please, help.
Here I create a package for functions:
private void BuildMessage(byte address, byte type, ushort start, ushort registers, ref byte[] message)
{
if (type == 3 || type == 16)
{
//Array to receive CRC bytes:
byte[] CRC = new byte[2];
message[0] = address;
message[1] = type;
message[2] = (byte)(start >> 8);
message[3] = (byte)start;
message[4] = (byte)(registers >> 8);
message[5] = (byte)registers;
GetCRC(message, ref CRC);
message[message.Length - 2] = CRC[0];
message[message.Length - 1] = CRC[1];
}
else if (type == 6)
{
byte[] CRC = new byte[2];
message[0] = address;
message[1] = type;
message[2] = (byte)(start >> 8);
message[3] = (byte)start;
message[4] = (byte)(registers >> 8);
message[5] = (byte)registers;
GetCRC(message, ref CRC);
message[6] = CRC[0];
message[7] = CRC[1];
}
}
This is my function number 3:
public bool SendFunc(int funcNumer, string connectType, byte address, ushort start, ushort registers, ref short[] values)
{
#region №3
if (funcNumer == 3)
{
#region serial-port
if (connectType.Equals("COM"))
{
//Ensure port is open:
if (sp.IsOpen)
{
//Clear in/out buffers:
sp.DiscardOutBuffer();
sp.DiscardInBuffer();
//Function 3 request is always 8 bytes:
byte[] message = new byte[8];
//Function 3 response buffer:
byte[] response = new byte[5 + 2 * registers];
//Build outgoing modbus message:
BuildMessage(address, (byte)3, start, registers, ref message);
//Send modbus message to Serial Port:
try
{
sp.Write(message, 0, message.Length);
GetResponse("COM", ref response);
}
catch (Exception err)
{
modbusStatus = "" + err.Message;
return false;
}
//Evaluate message:
if (CheckResponse(response))
{
//Return requested register values:
for (int i = 0; i < (response.Length - 5) / 2; i++)
{
values[i] = response[2 * i + 3];
values[i] <<= 8;
values[i] += response[2 * i + 4];
}
modbusStatus = "";
return true;
}
else
{
modbusStatus = "";
return false;
}
}
else
{
modbusStatus = "";
return false;
}
}
And here I am trying to implement function number 6:
if (funcNumer == 6)
{
#region serial-port
if (connectType.Equals("COM"))
{
//Ensure port is open:
if (sp.IsOpen)
{
//Clear in/out buffers:
sp.DiscardOutBuffer();
sp.DiscardInBuffer();
//Function 3 request is always 8 bytes:
byte[] message = new byte[8];
//Function 3 response buffer:
byte[] response = new byte[5 + 2 * registers];
//Build outgoing modbus message:
BuildMessage(address, (byte)6, start, registers, ref message);
//Send modbus message to Serial Port:
try
{
sp.Write(message, 0, message.Length);
GetResponse("COM", ref response);
}
catch (Exception err)
{
modbusStatus = "" + err.Message;
return false;
}
//Evaluate message:
if (CheckResponse(response))
{
//Return requested register values:
for (int i = 0; i < (response.Length - 5) / 2; i++)
{
values[i] = response[2 * i + 3];
values[i] <<= 8;
values[i] += response[2 * i + 4];
}
modbusStatus = "";
return true;
}
else
{
modbusStatus = "";
return false;
}
}
else
{
modbusStatus = "";
return false;
}
}
This is my function to check the response:
private bool CheckResponse(byte[] response)
{
//Perform a basic CRC check:
byte[] CRC = new byte[2];
GetCRC(response, ref CRC);
if (CRC[0] == response[response.Length - 2] && CRC[1] == response[response.Length - 1])
return true;
else
return false;
}
This is my function for get response:
private void GetResponse(string connect, ref byte[] response)
{
if (connect.Equals("COM"))
{
for (int i = 0; i < response.Length; i++)
{
response[i] = (byte)(sp.ReadByte());
}
}
else if (connect.Equals("TCP"))
{
NetworkStream stream = tcpClient.GetStream();
for (int i = 0; i < response.Length; i++)
{
response[i] = (byte)(stream.ReadByte());
}
}
else
{
}
}
The difference between Modbus function 0x03 and 0x06 is actually the part of the code you did not show on your question: CheckResponse(response).
Function 0x03 reads a number of registers, and the values in those registers (coming from the slave) are included in the response.
Function 0x06 writes a single register and gives an echo back. So the response is the same as the query.
With that information, it should be easy to modify your code: remove the for loop where you retrieve the register values.
Other than that you might need to modify your CheckResponse() function too, but that should also be quite straight forward: just check the response is exactly the same as the query (message).
EDIT: if your CheckResponse()` function only checks for the correct CRC on the responses I suppose you can keep it as it is.