DCB

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

At a Glance

Syntax

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;

Members

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:

fBinary

Specifies if binary mode is enabled. The Win32 API does not support nonbinary mode transfers, so this member must be TRUE. Using FALSE will not work.

fParity

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

fOutxCtsFlow

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

fOutxDsrFlow

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

fDtrControl

Specifies the DTR (data-terminal-ready) flow control. This member can be one of the following values:

fDsrSensitivity

Specifies if the communications driver is sensitive to the state of the DSR signal. If this member is TRUE, the driver ignores any bytes received, unless the DSR modem input line is high.

fTXContinueOnXoff

Specifies if transmission stops when the input buffer is full and the driver has transmitted the XoffChar character. If this member is 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 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 if XON/XOFF flow control is used during transmission. If this member is TRUE, transmission stops when the XoffChar character is received and starts again when the XonChar character is received.

fInX

Specifies if XON/XOFF flow control is used during reception. If this member is 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 if bytes received with parity errors are replaced with the character specified by the ErrorChar member. If this member is TRUE and the fParity member is TRUE, replacement occurs.

fNull

Specifies if null bytes are discarded. If this member is TRUE, null bytes are discarded when received.

fRtsControl

Specifies the RTS (request-to-send) flow control. If this value is zero, the default is RTS_CONTROL_HANDSHAKE. This member can be one of the following values:

fAbortOnError

Specifies if read and write operations are terminated if an error occurs. If this member is TRUE, the driver terminates all read and write operations with an error status if an error occurs. The driver will not accept any further communications operations until the application has acknowledged 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. It is one of the following values:

StopBits

Specifies the number of stop bits to be used. It is one of the following values:

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.

Remarks

For device driver developers: the COM_Open function in the sample serial port MDD driver does not support the fErrorChar, fNull, and fAbortOnChar members of the DCB structure. You are expected to add support for this functionality in your PDD layer, if appropriate for your serial port hardware.

The sample serial port MDD driver is found in Public\Common\Oak\Drivers\Serial.

See Also

ClearCommError, EscapeCommFunction, GetCommState, SetCommState