C# – Set DTR, RTS, CTS, DSR and Xonn/Xoff on SerialPort

cserial-port

I have this C++ code which I need to translate to C#.

 *hDev = CreateFile(PortNameUNC, GENERIC_READ|GENERIC_WRITE, 0, NULL, 
      OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

 if(*hDev == INVALID_HANDLE_VALUE) return false ;

DCB *dcb = new DCB ;
memset(dcb, 0x00, sizeof(DCB)) ;
dcb->DCBlength       = sizeof(DCB);
dcb->BaudRate        = BaudRate;
dcb->Parity          = Parity;
dcb->StopBits        = StopBits;
dcb->ByteSize        = ByteSize;
dcb->fBinary         = TRUE;
dcb->fDsrSensitivity = 0;
dcb->fDtrControl     = (DTR ? DTR_CONTROL_ENABLE : DTR_CONTROL_DISABLE) ;
dcb->fRtsControl     = (RTS ? RTS_CONTROL_ENABLE : RTS_CONTROL_DISABLE) ;
dcb->fOutxCtsFlow    = (CTS ? 1 : 0) ;
dcb->fOutxDsrFlow    = (DSR ? 1 : 0) ;
dcb->fOutX           = (XonnXoff ? 1 : 0) ;
dcb->fInX            = 0 ;

I managed to translate most of it on C# using e.g.

    m_port = new SerialPort(portName, baudRate, parity, dataBits, stopBits);

But I am not sure how to set properties like DTR, RTS, CTS, DSR and Xonn/Xoff?

I found Dtr.Enable and Rts.Enable properties on SerialPort, but what to do with other three? CTS, DSR and Xonn/Xoff? How to enable them?

EDIT: Also, here is my C# implementation of above. Have I correctly mapped the C++ code to C# as below? any feedback appreciated. especially the xon/xoff flags and the dtr and rts?

 public SerialPortHASP(string portName, int baudRate, Parity parity, int dataBits, StopBits stopBits, bool dtr, bool rts, bool xonxoff)
    {

        m_port = new SerialPort(portName, baudRate, parity, dataBits, stopBits);

        // Set XonXoff if set
        if (xonxoff)
            m_port.Handshake = Handshake.XOnXOff;

        // Set DTR/RTS
        m_port.DtrEnable = dtr;
        m_port.RtsEnable = rts;

        // Open the port for communications
        m_port.Open();
    }

Best Answer

CTS and DSR are inputs so they can't be set from code. They can be checked by accessing the following properties; CtsHolding and DsrHolding.

XOnXOff is a flow control and can be set using the serial ports Handshake property.

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

.net – Error opening serial port using the System.IO.Ports.SerialPort class

Regarding the differences between HyperTerminal and the .NET serial port object, HyperTerminal is a commercial, stable application. If the underlying serial port object died or threw an exception, HyperTerminal hid it from you. The .NET serial port object throws more exceptions than any other .NET object I've used.

Points to make:

Whenever you change a setting, close it first, change it, then re-open it. Some ports really hate it when you change it while open.
Expect to do a lot of 'try-catch's around your serial port object, around every thing you do.
Make sure you have one for each possible exception listed, and make sure each one checks the message (it can be different under different circumstances). Many are recoverable simply by closing and reopening.
Try following exactly where the exceptions are being thrown. See if modifying the order you set things fixes it ... the object is really finicky.

If you've tried explicitly setting DTR to false before opening, then you may just have to grin and bear it with that device. The SerialPort object is not one of the glowing examples of a well implemented library in .NET. If you notice, HyperTerminal gets that same error, but it just ignores it.

If you can, try it with a regular serial port or a different brand USB device. If you still get the same error, it might be something on your application side.