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DCB

Windows Mobile 6.5
A version of this page is also available for
4/8/2010

This structure defines the control setting for a serial communications device.


typedef struct _DCB {
  DWORD DCBlength;
  DWORD BaudRate; 
  DWORD fBinary :1;
  DWORD fParity :1;
  DWORD fOutxCtsFlow :1;
  DWORD fOutxDsrFlow :1;
  DWORD fDtrControl :2;
  DWORD fDsrSensitivity :1;
  DWORD fTXContinueOnXoff :1;
  DWORD fOutX :1;
  DWORD fInX :1;
  DWORD fErrorChar :1;
  DWORD fNull :1;
  DWORD fRtsControl :2;
  DWORD fAbortOnError :1;
  DWORD fDummy2 :17;
  WORD wReserved;
  WORD XonLim;
  WORD XoffLim;
  BYTE ByteSize;
  BYTE Parity;
  BYTE StopBits;
  char XonChar;
  char XoffChar;
  char ErrorChar;
  char EofChar;
  char EvtChar;
  WORD wReserved1;
} DCB, *LPDCB;

DCBlength

Specifies the DCB structure length, in bytes.

BaudRate

Specifies the baud rate at which the communication device operates. It is an actual baud rate value, or one of the following baud rate indexes:

  • CBR_110
  • CBR_300
  • CBR_600
  • CBR_1200
  • CBR_2400
  • CBR_4800
  • CBR_9600
  • CBR_14400
  • CBR_19200
  • CBR_38400
  • CBR_56000
  • CBR_57600
  • CBR_115200
  • CBR_128000
  • CBR_256000
fBinary

Specifies whether binary mode is enabled. The function does not support nonbinary mode transfers, so this member must be set to TRUE.

fParity

Specifies whether parity checking is enabled. If this member is set to TRUE, parity checking is performed, and errors are reported.

fOutxCtsFlow

Specifies if the clear-to-send (CTS) signal is monitored for output flow control. If this member is set to TRUE and CTS is turned off, output is suspended until CTS is sent again.

fOutxDsrFlow

Specifies if the data-set-ready (DSR) signal is monitored for output flow control. If this member is set to TRUE and DSR is turned off, output is suspended until DSR is sent again.

fDtrControl

Specifies the data-terminal-ready (DTR) flow control. The following table shows possible values.

Value Description

DTR_CONTROL_DISABLE

Disables the DTR line when the device is opened and leaves it disabled.

DTR_CONTROL_ENABLE

Enables the DTR line when the device is opened and leaves it on.

DTR_CONTROL_HANDSHAKE

Enables DTR handshaking.

If handshaking is enabled, it is an error for the application to adjust the line by using the EscapeCommFunction function.

fDsrSensitivity

Specifies whether the communications driver is sensitive to the state of the data-send-ready (DSR) signal. If this member is set to TRUE, the driver ignores bytes received, unless the DSR modem input line is high.

fTXContinueOnXoff

Specifies whether transmission stops when the input buffer is full and the driver has transmitted the XoffChar character. If this member is set to TRUE, transmission continues after the input buffer has come within XoffLim bytes of being full and the driver has transmitted the XoffChar character to stop receiving bytes.

If this member is set to FALSE, transmission does not continue until the input buffer is within XonLim bytes of being empty and the driver has transmitted the XonChar character to resume reception.

fOutX

Specifies whether XON/XOFF flow control is used during transmission. If this member is set to TRUE, transmission stops when the XoffChar character is received and starts again when the XonChar character is received.

fInX

Specifies whether XON/XOFF flow control is used during reception. If this member is set to TRUE, the XoffChar character is sent when the input buffer comes within XoffLim bytes of being full, and the XonChar character is sent when the input buffer comes within XonLim bytes of being empty.

fErrorChar

Specifies whether bytes received with parity errors are replaced with the character specified by the ErrorChar member. If this member is set to TRUE and the fParity member is set to TRUE, replacement occurs.

fNull

Specifies whether null bytes are discarded. If this member is set to TRUE, null bytes are discarded when received.

fRtsControl

Specifies the request-to-send (RTS) flow control. If this value is set to zero, the default is RTS_CONTROL_HANDSHAKE. The following table shows possible values.

Value Description

RTS_CONTROL_DISABLE

Disables the RTS line when the device is opened and leaves it disabled.

RTS_CONTROL_ENABLE

Enables the RTS line when the device is opened and leaves it on.

RTS_CONTROL_HANDSHAKE

Enables RTS handshaking.

The driver raises the RTS line when the type-ahead (input) buffer is less than half full and lowers the RTS line when the buffer is more than three-quarters full.

If handshaking is enabled, it is an error for the application to adjust the line by using the EscapeCommFunction function.

RTS_CONTROL_TOGGLE

Specifies that the RTS line is high if bytes are available for transmission.

After all buffered bytes are sent, the RTS line is low.

fAbortOnError

Specifies whether read and write operations are terminated if an error occurs. If this member is set to TRUE, the driver terminates all read and write operations with an error status if an error occurs. The driver does not accept further communications operations until the application acknowledges the error by calling the ClearCommError function.

fDummy2

Reserved; do not use.

wReserved

Not used; set to zero.

XonLim

Specifies the minimum number of bytes accepted in the input buffer before the XON character is sent.

XoffLim

Specifies the maximum number of bytes accepted in the input buffer before the XOFF character is sent. The maximum number of bytes accepted is calculated by subtracting this value from the size, in bytes, of the input buffer.

ByteSize

Specifies the number of bits in the bytes transmitted and received.

Parity

Specifies the parity scheme to be used. The following table shows possible values.

Value Description

EVENPARITY

Even

MARKPARITY

Mark

NOPARITY

No parity

ODDPARITY

Odd

SPACEPARITY

Space

StopBits

Specifies the number of stop bits to be used. The following table shows possible values.

Value Description

ONESTOPBIT

1 stop bit

ONE5STOPBITS

1.5 stop bits

TWOSTOPBITS

2 stop bits

XonChar

Specifies the value of the XON character for both transmission and reception.

XoffChar

Specifies the value of the XOFF character for both transmission and reception.

ErrorChar

Specifies the value of the character used to replace bytes received with a parity error.

EofChar

Specifies the value of the character used to signal the end of data.

EvtChar

Specifies the value of the character used to signal an event.

wReserved1

Reserved; do not use.

The sample serial port PDD driver is in the %_WINCEROOT%\Public\Common\Oak\Drivers\Serial directory.

All directories under the Serial folder contain sample serial PDD drivers except for the COM_MDD and COM_MDD2 folders.

Headerwinbase.h
Windows Embedded CEWindows CE 1.0 and later
Windows MobileWindows Mobile Version 5.0 and later

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