public static bool DetectFrame(byte unitIdentifier, Memory <byte> frame)
{
byte newUnitIdentifier;
/* Correct response frame (min. 6 bytes)
* 00 Unit Identifier
* 01 Function Code
* 02 Byte count
* 03 Minimum of 1 byte
* 04 CRC Byte 1
* 05 CRC Byte 2
*/
/* Error response frame (5 bytes)
* 00 Unit Identifier
* 01 Function Code + 0x80
* 02 Exception Code
* 03 CRC Byte 1
* 04 CRC Byte 2
*/
var span = frame.Span;
if (span.Length < 5)
{
return(false);
}
if (unitIdentifier != 255) // 255 means "skip unit identifier check"
{
newUnitIdentifier = span[0];
if (newUnitIdentifier != unitIdentifier)
{
return(false);
}
}
// CRC check
var crcBytes = span.Slice(span.Length - 2, 2);
var actualCRC = unchecked ((ushort)((crcBytes[1] << 8) + crcBytes[0]));
var expectedCRC = ModbusUtils.CalculateCRC(frame.Slice(0, frame.Length - 2));
if (actualCRC != expectedCRC)
{
return(false);
}
return(true);
}
protected override int WriteFrame(Action extendFrame)
{
int frameLength;
ushort crc;
this.FrameBuffer.Writer.Seek(0, SeekOrigin.Begin);
// add unit identifier
this.FrameBuffer.Writer.Write(this.UnitIdentifier);
// add PDU
extendFrame();
// add CRC
frameLength = unchecked ((int)this.FrameBuffer.Writer.BaseStream.Position);
crc = ModbusUtils.CalculateCRC(this.FrameBuffer.Buffer.AsMemory(0, frameLength));
this.FrameBuffer.Writer.Write(crc);
return(frameLength + 2);
}
private protected override Span <byte> TransceiveFrame(byte unitIdentifier, ModbusFunctionCode functionCode, Action <ExtendedBinaryWriter> extendFrame)
{
int messageLength;
int frameLength;
byte rawFunctionCode;
ushort crc;
int mbapHeaderLength = 4;
// build request
if (!(0 <= unitIdentifier && unitIdentifier <= 247))
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidUnitIdentifier);
}
// special case: broadcast (only for write commands)
if (unitIdentifier == 0)
{
switch (functionCode)
{
case ModbusFunctionCode.WriteMultipleRegisters:
case ModbusFunctionCode.WriteSingleCoil:
case ModbusFunctionCode.WriteSingleRegister:
case ModbusFunctionCode.WriteMultipleCoils:
case ModbusFunctionCode.WriteFileRecord:
case ModbusFunctionCode.MaskWriteRegister:
break;
default:
throw new ModbusException(ErrorMessage.Modbus_InvalidUseOfBroadcast);
}
}
_frameBuffer.Writer.Seek(0, SeekOrigin.Begin);
_frameBuffer.Writer.Write(unitIdentifier); // 00 Unit Identifier
extendFrame(_frameBuffer.Writer);
frameLength = (int)_frameBuffer.Writer.BaseStream.Position;
// add CRC
crc = ModbusUtils.CalculateCRC(_frameBuffer.Buffer.AsMemory().Slice(0, frameLength));
_frameBuffer.Writer.Write(crc);
frameLength = (int)_frameBuffer.Writer.BaseStream.Position;
// build message
_messageBuffer.Writer.Seek(0, SeekOrigin.Begin);
if (!SwapBytes)
{
_messageBuffer.Writer.WriteReverse(ProtocolIdentifier); //2b
_messageBuffer.Writer.WriteReverse((ushort)frameLength); //2b
}
else
{
_messageBuffer.Writer.Write(ProtocolIdentifier); //2b
_messageBuffer.Writer.Write((ushort)frameLength); //2b
}
_messageBuffer.Writer.Write(_frameBuffer.Buffer, 0, frameLength); //framelength
messageLength = frameLength + mbapHeaderLength;
// send request
_serialPort.Write(_messageBuffer.Buffer, 0, messageLength);
// special case: broadcast (only for write commands)
if (unitIdentifier == 0)
{
return(_messageBuffer.Buffer.AsSpan(0, 0));
}
// wait for and process response
messageLength = 0;
_messageBuffer.Reader.BaseStream.Seek(0, SeekOrigin.Begin);
while (true)
{
messageLength += _serialPort.Read(_messageBuffer.Buffer, messageLength, _messageBuffer.Buffer.Length - messageLength);
if (ModbusUtils.DetectFrame(unitIdentifier, _messageBuffer.Buffer.AsMemory().Slice(mbapHeaderLength, messageLength - mbapHeaderLength)))
{
break;
}
else
{
// reset length because one or more chunks of data were received and written to
// the buffer, but no valid Modbus frame could be detected and now the buffer is full
if (messageLength == _messageBuffer.Buffer.Length)
{
messageLength = 0;
}
}
}
//write message content to framebuffer
_frameBuffer.Writer.BaseStream.Seek(0, SeekOrigin.Begin);
_frameBuffer.Writer.Write(_messageBuffer.Buffer.AsSpan().Slice(mbapHeaderLength).ToArray(), 0, messageLength - mbapHeaderLength);
frameLength = messageLength - mbapHeaderLength;
unitIdentifier = _frameBuffer.Reader.ReadByte();
rawFunctionCode = _frameBuffer.Reader.ReadByte();
if (rawFunctionCode == (byte)ModbusFunctionCode.Error + (byte)functionCode)
{
this.ProcessError(functionCode, (ModbusExceptionCode)_frameBuffer.Buffer[2]);
}
else if (rawFunctionCode != (byte)functionCode)
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidResponseFunctionCode);
}
return(_frameBuffer.Buffer.AsSpan(1, frameLength - 3));
}
private protected override async Task <Memory <byte> > TransceiveFrameAsync(byte unitIdentifier, ModbusFunctionCode functionCode, Action <ExtendedBinaryWriter> extendFrame, CancellationToken cancellationToken = default)
{
int frameLength;
byte rawFunctionCode;
ushort crc;
// build request
if (!(0 <= unitIdentifier && unitIdentifier <= 247))
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidUnitIdentifier);
}
// special case: broadcast (only for write commands)
if (unitIdentifier == 0)
{
switch (functionCode)
{
case ModbusFunctionCode.WriteMultipleRegisters:
case ModbusFunctionCode.WriteSingleCoil:
case ModbusFunctionCode.WriteSingleRegister:
case ModbusFunctionCode.WriteMultipleCoils:
case ModbusFunctionCode.WriteFileRecord:
case ModbusFunctionCode.MaskWriteRegister:
break;
default:
throw new ModbusException(ErrorMessage.Modbus_InvalidUseOfBroadcast);
}
}
_frameBuffer.Writer.Seek(0, SeekOrigin.Begin);
_frameBuffer.Writer.Write(unitIdentifier); // 00 Unit Identifier
extendFrame(_frameBuffer.Writer);
frameLength = (int)_frameBuffer.Writer.BaseStream.Position;
// add CRC
crc = ModbusUtils.CalculateCRC(_frameBuffer.Buffer.AsMemory().Slice(0, frameLength));
_frameBuffer.Writer.Write(crc);
frameLength = (int)_frameBuffer.Writer.BaseStream.Position;
// send request
await _serialPort.WriteAsync(_frameBuffer.Buffer, 0, frameLength, cancellationToken).ConfigureAwait(false);
// special case: broadcast (only for write commands)
if (unitIdentifier == 0)
{
return(_frameBuffer.Buffer.AsMemory(0, 0));
}
// wait for and process response
frameLength = 0;
_frameBuffer.Reader.BaseStream.Seek(0, SeekOrigin.Begin);
while (true)
{
frameLength += await _serialPort.ReadAsync(_frameBuffer.Buffer, frameLength, _frameBuffer.Buffer.Length - frameLength, cancellationToken).ConfigureAwait(false);
if (ModbusUtils.DetectFrame(unitIdentifier, _frameBuffer.Buffer.AsMemory().Slice(0, frameLength)))
{
break;
}
else
{
// reset length because one or more chunks of data were received and written to
// the buffer, but no valid Modbus frame could be detected and now the buffer is full
if (frameLength == _frameBuffer.Buffer.Length)
{
frameLength = 0;
}
}
}
unitIdentifier = _frameBuffer.Reader.ReadByte();
rawFunctionCode = _frameBuffer.Reader.ReadByte();
if (rawFunctionCode == (byte)ModbusFunctionCode.Error + (byte)functionCode)
{
this.ProcessError(functionCode, (ModbusExceptionCode)_frameBuffer.Buffer[2]);
}
else if (rawFunctionCode != (byte)functionCode)
{
throw new ModbusException(ErrorMessage.ModbusClient_InvalidResponseFunctionCode);
}
return(_frameBuffer.Buffer.AsMemory(1, frameLength - 3));
}
