Error opening serial port

Question

I'm trying to open and read from a serial port using the System.IO.Ports.SerialPort class. I dragged the serial port from the tool pane (VS 2008) on to my windows form. I've got a property grid set up so I can easily change properties of the serial port at runtime. When I try to open the port, I get the error shown below. I don't understand why because I can open and read from the port using Hyperterminal. Any ideas?

System.IO.IOException Error connection: A device attached to the system is not functioning
   at System.IO.Ports.InternalResources.WinIOError(Int32 errorCode, String str)
   at System.IO.Ports.InternalResources.WinIOError()
   at System.IO.Ports.SerialStream.set_DtrEnable(Boolean value)
   at System.IO.Ports.SerialStream..ctor(String portName, Int32 baudRate, Parity parity, Int32 dataBits, StopBits stopBits, Int32 readTimeout, Int32 writeTimeout, Handshake handshake, Boolean dtrEnable, Boolean rtsEnable, Boolean discardNull, Byte parityReplace)
   at System.IO.Ports.SerialPort.Open()
   at Test.CardReader.frmMain.Connect() in D:\Develop\2.0\Projects\Kiosk\EmbeddedBrowser\Windows Forms\Test.CardReader\Form1.cs:line 166

Note, this is a USB connection so it's actuall a virtual serial port My settings are as follows:
BaudRate = 9600
DataBits = 8
DiscardNull = false
DtrEnable = false
Handshake = None
Parity = None
ParityReplace = 63
PortName = COM3
ReadBufferSize = 4096
ReadTimeout = -1
ReceivedBytes = 1
TrsEnable = False
StopBits = One
WriteBufferSize = 2048
WriteTimeout = -1

I downloaded PortMon from sysinternals. I've captured 2 logs, the first is the log how what happens when Hyperterminal opens the port, the second is what happends when The .net SerialPort class tries to open the port:

Hyperterminal:

IRP_MJ_CREATE                   USBSER000   SUCCESS         Options: Open 
IOCTL_SERIAL_SET_QUEUE_SIZE     USBSER000 SUCCESS         InSize: 8192 OutSize: 8192
IOCTL_SERIAL_CONFIG_SIZE        USBSER000 SUCCESS         Size: 0
IOCTL_SERIAL_GET_BAUD_RATE      USBSER000 SUCCESS 
IOCTL_SERIAL_GET_LINE_CONTROL   USBSER000 SUCCESS 
IOCTL_SERIAL_GET_CHARS          USBSER000 SUCCESS 
IOCTL_SERIAL_GET_HANDFLOW       USBSER000 SUCCESS 
IOCTL_SERIAL_GET_BAUD_RATE      USBSER000 SUCCESS 
IOCTL_SERIAL_GET_LINE_CONTROL   USBSER000 SUCCESS 
IOCTL_SERIAL_GET_CHARS          USBSER000 SUCCESS 
IOCTL_SERIAL_GET_HANDFLOW       USBSER000 SUCCESS 
IOCTL_SERIAL_SET_BAUD_RATE      USBSER000 SUCCESS         Rate: 9600
IOCTL_SERIAL_SET_RTS            USBSER000 SUCCESS 
IOCTL_SERIAL_SET_DTR            USBSER000 * 0xC0000001 
IOCTL_SERIAL_SET_LINE_CONTROL   USBSER000 SUCCESS         StopBits: 1 Parity: NONE WordLength: 8
IOCTL_SERIAL_SET_CHAR           USBSER000 SUCCESS         EOF:1a ERR:0 BRK:0 EVT:1a XON:f6 XOFF:6
IOCTL_SERIAL_SET_HANDFLOW       USBSER000 SUCCESS         Shake:80000001 Replace:80000040 XonLimit:80 XoffLimit:200
IOCTL_SERIAL_SET_TIMEOUTS       USBSER000 SUCCESS         RI:10 RM:0 RC:0 WM:0 WC:5000
IOCTL_SERIAL_SET_WAIT_MASK      USBSER000 SUCCESS         Mask: RLSD ERR 
IOCTL_SERIAL_GET_MODEMSTATUS    USBSER000 SUCCESS 
IOCTL_SERIAL_WAIT_ON_MASK       USBSER000  
IRP_MJ_READ USBSER000                                  Length 80

.Net SerialPort:

IRP_MJ_CREATE                   USBSER000   SUCCESS Options: Open 
IOCTL_SERIAL_GET_PROPERTIES     USBSER000 SUCCESS 
IOCTL_SERIAL_GET_MODEMSTATUS    USBSER000 SUCCESS 
IOCTL_SERIAL_GET_BAUD_RATE      USBSER000 SUCCESS 
IOCTL_SERIAL_GET_LINE_CONTROL   USBSER000 SUCCESS 
IOCTL_SERIAL_GET_CHARS          USBSER000 SUCCESS 
IOCTL_SERIAL_GET_HANDFLOW       USBSER000 SUCCESS 
IOCTL_SERIAL_GET_BAUD_RATE      USBSER000 SUCCESS 
IOCTL_SERIAL_GET_LINE_CONTROL   USBSER000 SUCCESS 
IOCTL_SERIAL_GET_CHARS          USBSER000 SUCCESS 
IOCTL_SERIAL_GET_HANDFLOW       USBSER000 SUCCESS 
IOCTL_SERIAL_SET_BAUD_RATE      USBSER000 SUCCESS Rate: 9600
IOCTL_SERIAL_CLR_RTS            USBSER000 SUCCESS 
IOCTL_SERIAL_CLR_DTR            USBSER000 * 0xC0000001 
IOCTL_SERIAL_SET_LINE_CONTROL   USBSER000   SUCCESS StopBits: 1 Parity: NONE WordLength: 8
IOCTL_SERIAL_SET_CHAR           USBSER000 SUCCESS EOF:1a ERR:0 BRK:0 EVT:1a XON:11 XOFF:13
IOCTL_SERIAL_SET_HANDFLOW       USBSER000   SUCCESS Shake:0 Replace:0 XonLimit:4096 XoffLimit:4096
IOCTL_SERIAL_GET_BAUD_RATE      USBSER000   SUCCESS 
IOCTL_SERIAL_GET_LINE_CONTROL   USBSER000   SUCCESS 
IOCTL_SERIAL_GET_CHARS          USBSER000   SUCCESS 
IOCTL_SERIAL_GET_HANDFLOW       USBSER000   SUCCESS 
IOCTL_SERIAL_SET_BAUD_RATE      USBSER000   SUCCESS Rate: 9600
IOCTL_SERIAL_CLR_RTS            USBSER000   SUCCESS 
IOCTL_SERIAL_CLR_DTR            USBSER000   * 0xC0000001 
IOCTL_SERIAL_SET_LINE_CONTROL   USBSER000   SUCCESS StopBits: 1 Parity: NONE WordLength: 8
IOCTL_SERIAL_SET_CHAR           USBSER000   SUCCESS EOF:1a ERR:0 BRK:0 EVT:1a XON:11 XOFF:13
IOCTL_SERIAL_SET_HANDFLOW       USBSER000   SUCCESS Shake:0 Replace:0 XonLimit:4096 XoffLimit:4096
IOCTL_SERIAL_CLR_DTR            USBSER000   * 0xC0000001 
IRP_MJ_CLEANUP                  USBSER000   SUCCESS 
IRP_MJ_CLOSE                    USBSER000   SUCCESS

Answer 1

From MSDN:

IOException:

The port is in an invalid state.

or -

An attempt to set the state of the underlying port failed. For example, the parameters passed from this SerialPort object were invalid.

What parameters did you pass to the port (baud rate, bits, stop bits, parity)? Perhaps one of those values was invalid.

Answer 2

In real UART, DTREnable will assert the DTR pin of your UART to indicate you are ready to receive data.

Depending on your driver's implementation, you may need to set DTREnable to true to open the port.

Answer 3

See this forum post. I suspect it has to do with the hardware or the driver malfunctioning. This doesn't explain why it works with Hyperterminal though. Follow the advice from Joseph M. Newcomer to see what Hyperterminal is doing differently.

Answer 4

Regarding the differences between hyperterminal and the .NET serial port object, Hyperterminal is a commercial, stable app. 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 bare 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 app side.

Answer 5

it looks like the difference is the handshaking.

i haven't had problems with the serialport class and have written apps that ran at 800,000 bps.