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| <h4 class="subsection">17.4.6 Control Modes</h4> |
| |
| <p>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 <code>c_cflag</code> member of the <code>struct |
| termios</code> structure. |
| |
| <p>The <code>c_cflag</code> member itself is an integer, and you change the flags |
| and fields using the operators <code>&</code>, <code>|</code>, and <code>^</code>. Don't |
| try to specify the entire value for <code>c_cflag</code>—instead, change |
| only specific flags and leave the rest untouched (see <a href="Setting-Modes.html#Setting-Modes">Setting Modes</a>). |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CLOCAL</b><var><a name="index-CLOCAL-1888"></a></var><br> |
| <blockquote><p>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. |
| <a name="index-modem-status-lines-1889"></a><a name="index-carrier-detect-1890"></a> |
| On many systems if this bit is not set and you call <code>open</code> without |
| the <code>O_NONBLOCK</code> flag set, <code>open</code> blocks until a modem |
| connection is established. |
| |
| <p>If this bit is not set and a modem disconnect is detected, a |
| <code>SIGHUP</code> signal is sent to the controlling process group for the |
| terminal (if it has one). Normally, this causes the process to exit; |
| see <a href="Signal-Handling.html#Signal-Handling">Signal Handling</a>. Reading from the terminal after a disconnect |
| causes an end-of-file condition, and writing causes an <code>EIO</code> error |
| to be returned. The terminal device must be closed and reopened to |
| clear the condition. |
| <a name="index-modem-disconnect-1891"></a></p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>HUPCL</b><var><a name="index-HUPCL-1892"></a></var><br> |
| <blockquote><p>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. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CREAD</b><var><a name="index-CREAD-1893"></a></var><br> |
| <blockquote><p>If this bit is set, input can be read from the terminal. Otherwise, |
| input is discarded when it arrives. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CSTOPB</b><var><a name="index-CSTOPB-1894"></a></var><br> |
| <blockquote><p>If this bit is set, two stop bits are used. Otherwise, only one stop bit |
| is used. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>PARENB</b><var><a name="index-PARENB-1895"></a></var><br> |
| <blockquote><p>If this bit is set, generation and detection of a parity bit are enabled. |
| See <a href="Input-Modes.html#Input-Modes">Input Modes</a>, for information on how input parity errors are handled. |
| |
| <p>If this bit is not set, no parity bit is added to output characters, and |
| input characters are not checked for correct parity. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>PARODD</b><var><a name="index-PARODD-1896"></a></var><br> |
| <blockquote><p>This bit is only useful if <code>PARENB</code> is set. If <code>PARODD</code> is set, |
| odd parity is used, otherwise even parity is used. |
| </p></blockquote></div> |
| |
| <p>The control mode flags also includes a field for the number of bits per |
| character. You can use the <code>CSIZE</code> macro as a mask to extract the |
| value, like this: <code>settings.c_cflag & CSIZE</code>. |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CSIZE</b><var><a name="index-CSIZE-1897"></a></var><br> |
| <blockquote><p>This is a mask for the number of bits per character. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CS5</b><var><a name="index-CS5-1898"></a></var><br> |
| <blockquote><p>This specifies five bits per byte. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CS6</b><var><a name="index-CS6-1899"></a></var><br> |
| <blockquote><p>This specifies six bits per byte. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CS7</b><var><a name="index-CS7-1900"></a></var><br> |
| <blockquote><p>This specifies seven bits per byte. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CS8</b><var><a name="index-CS8-1901"></a></var><br> |
| <blockquote><p>This specifies eight bits per byte. |
| </p></blockquote></div> |
| |
| <p>The following four bits are BSD extensions; this exist only on BSD |
| systems and the GNU system. |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CCTS_OFLOW</b><var><a name="index-CCTS_005fOFLOW-1902"></a></var><br> |
| <blockquote><p>If this bit is set, enable flow control of output based on the CTS wire |
| (RS232 protocol). |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CRTS_IFLOW</b><var><a name="index-CRTS_005fIFLOW-1903"></a></var><br> |
| <blockquote><p>If this bit is set, enable flow control of input based on the RTS wire |
| (RS232 protocol). |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>MDMBUF</b><var><a name="index-MDMBUF-1904"></a></var><br> |
| <blockquote><p>If this bit is set, enable carrier-based flow control of output. |
| </p></blockquote></div> |
| |
| <!-- termios.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: tcflag_t <b>CIGNORE</b><var><a name="index-CIGNORE-1905"></a></var><br> |
| <blockquote><p>If this bit is set, it says to ignore the control modes and line speed |
| values entirely. This is only meaningful in a call to <code>tcsetattr</code>. |
| |
| <p>The <code>c_cflag</code> member and the line speed values returned by |
| <code>cfgetispeed</code> and <code>cfgetospeed</code> will be unaffected by the |
| call. <code>CIGNORE</code> is useful if you want to set all the software |
| modes in the other members, but leave the hardware details in |
| <code>c_cflag</code> unchanged. (This is how the <code>TCSASOFT</code> flag to |
| <code>tcsettattr</code> works.) |
| |
| <p>This bit is never set in the structure filled in by <code>tcgetattr</code>. |
| </p></blockquote></div> |
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