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Control Modes

This section describes the terminal flags and fields that control parameters usually associated with asynchronous serial data transmission. These flags may not make sense for other kinds of terminal ports (such as a network connection pseudo-terminal). All of these are contained in the c_cflag member of the struct termios structure.

The c_cflag member itself is an integer, and you change the flags and fields using the operators &, |, and ^. Don't try to specify the entire value for c_cflag---instead, change only specific flags and leave the rest untouched (see section Setting Terminal Modes Properly).

CLOCAL

If this bit is set, it indicates that the terminal is connected "locally" and that the modem status lines (such as carrier detect) should be ignored.

If this bit is not set and you call open without the O_NONBLOCK flag set, open blocks until a modem connection is established.

If this bit is not set and a modem disconnect is detected, a SIGHUP signal is sent to the controlling process group for the terminal (if it has one). Normally, this causes the process to exit; see section Signal Handling. Reading from the terminal after a disconnect causes an end-of-file condition, and writing causes an EIO error to be returned. The terminal device must be closed and reopened to clear the condition.

HUPCL

If this bit is set, a modem disconnect is generated when all processes that have the terminal device open have either closed the file or exited.

CREAD

If this bit is set, input can be read from the terminal. Otherwise, input is discarded when it arrives.

CSTOPB

If this bit is set, two stop bits are used. Otherwise, only one stop bit is used.

PARENB

If this bit is set, generation and detection of a parity bit are enabled. See section Input Modes, for information on how input parity errors are handled.

If this bit is not set, no parity bit is added to output characters, and input characters are not checked for correct parity.

PARODD

This bit is only useful if PARENB is set. If PARODD is set, odd parity is used, otherwise even parity is used.

The control mode flags also includes a field for the number of bits per character. You can use the CSIZE macro as a mask to extract the value, like this: settings.c_cflag & CSIZE.

CSIZE

This is a mask for the number of bits per character.

CS5

This specifies five bits per byte.

CS6

This specifies six bits per byte.

CS7

This specifies seven bits per byte.

CS8

This specifies eight bits per byte.

CCTS_OFLOW

If this bit is set, enable flow control of output based on the CTS wire (RS232 protocol).

CRTS_IFLOW

If this bit is set, enable flow control of input based on the RTS wire (RS232 protocol).

MDMBUF

If this bit is set, enable carrier-based flow control of output.

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