UM0851 datasheet(103/245 Pages) STMICROELECTRONICS

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UM0851

Communication device drivers

Doc ID 16604 Rev 2

103/245

Writing data to the port is easy, just use the write() system call to send data:

/* The write() function returns the number of bytes sent or -1 if an error

occurred.

fd: file descriptor

buf: character array

n: number of bytes to be transferred */

write(int fd, char *buf, int n);

Reading data from a port is a little trickier. When you operate the port in raw data mode,

each read() system call returns the number of characters that are actually available in the

serial input buffers. If no characters are available, the call blocks (waits) until characters

come in, an interval timer expires, or an error occurs.

Reading data from the port

/* fd: file descriptor

buf: character array

n: number of bytes to be transferred */

read(int fd, char *buf, int n);

Closing a serial port

Close disassociates a TTY from its underlying device and resets the TTY's device control

block. When the port is closed for the last time you can do the proper hardware shutdown

and free any allocated memory.

To close the serial port, just use the close system call:

int fd;

/* fd: file descriptor */

close(fd);

Application code

The test code given below uses the open(), read(), ioctl() and close() functions. The serial

port ttyS0 is opened and later it receives the data when the read() function is called. The

input and output port baud rate can be also configured in the code by using the

cfsetispeed() and cfsetospeed() functions.

#include<stdio.h>

#include<fcntl.h>

#include<termios.h>

main()

{

int fd;

char s[10];

fd=open("/dev/ttyS0", O_RDWR, 0);

if(fd < 0)

return -1;

struct termios options;

/*Get the current options for the port......*/

ioctl(fd,TCGETS,&options);

/*Set the baud rates........................*/

cfsetispeed(&options, B115200);

cfsetospeed(&options, B115200);

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