UM0851 datasheet(102/245 Pages) STMICROELECTRONICS

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Communication device drivers

UM0851

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Doc ID 16604 Rev 2

/* Set the baud rate to 115200 baud */

cfsetispeed (&termios, B115200); /* Set the terminal output baud rate */

cfsetospeed (&termios, B115200); /* Set the terminal input baud rate */

/* TCSETS and the struct termios sets all the current termios parameters. */

ioctl (fd, TCSETS, &termios);

Getting the control signals

The TIOCMGET ioctl() gets the current "MODEM" status bits, which consist of all of the RS-

232 signal lines except RXD and TXD, listed in Table 33.

To get the status bits, call ioctl() with a pointer to an integer to hold the bits.

Getting the MODEM status bits

int fd;

int status;

ioctl(fd, TIOCMGET, &status);

Setting the control signals

The TIOCMSET ioctl sets the modem status bits defined above. To drop the DTR signal you

can use the code listed below:

int fd;

int status;

ioctl(fd, TIOCMGET, &status);

status &= ~TIOCM_DTR;

ioctl(fd, TIOCMSET, &status);

The bits that can be set depend on the operating system, driver, and modes in use.

Writing data to a port

When data is to be sent to the hardware, the write function is called. This function returns

the number of characters that are actually written to the device.

Table 33.

Control signal constants

Constant

Description

TIOCM_LE

DSR (data set ready/line enable)

TIOCM_DTR

DTR (data terminal ready)

TIOCM_RTS

RTS (request to send)

TIOCM_ST

Secondary TXD (transmit)

TIOCM_SR

Secondary RXD (receive)

TIOCM_CTS

CTS (clear to send)

TIOCM_CAR

DCD (data carrier detect)

TIOCM_CD

Synonym for TIOCM_CAR

TIOCM_RNG

RNG (ring)

TIOCM_RI

Synonym for TIOCM_RNG

TIOCM_DSR

DSR (data set ready)

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