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Lab04 - Serial port access

Use cat and picocom for serial line access.


cat allows to read data from a file or device. The Nucleo board will be present at /dev/ttyACM0. The default speed of the serial port set by the kernel driver is 115200 bd.

cat /dev/ttyACM0

The main issue with serial communication is the proper settings of the communication paramters such as:

  • communication speed - baudrate
  • number of bites - usually 8
  • number of stop-bits - usually 1
  • parity - in some applications none

Unix environment allows to control the serial line settings by stty command.

stty -F /dev/ttyS0 9600 cs8 -cstopb -parenb


  • Set the proper parameters of the communication device by stty command
  • Display the readings from the Nucleo board and demonstrate the Nucleo board returns different reply for different characters. When entering:
    • 'w' the board will reply by “Welcome to the Nucleo STM32F401RE” and when entering
    • 'a' the board will reply by your name
    • 'i' the board will reply by a random character


Perform the same task with picocom terminal (help man piccocom).

C app

Use the application from HW01 and add functionality which opens the serial device and allows you to send and receive data from the board.

Serial port open

int hSerial = open( "/dev/ttyUSB0", O_RDWR| O_NONBLOCK | O_NDELAY );
// h = handle

Serial port settings

struct termios o_tty;
// o = object
memset (&o_tty, 0, sizeof o_tty);
iRetVal = tcgetattr (hSerial , &o_tty);
Now, modify the settings appropriately.

Serial port write

unsigned char chArrCmd[] = {'*', 'I', 'D', 'N', '?', '\r', '\n', '\0'};
int n_written = write( hSerial, chArrCmd, sizeof(chArrCmd)-1 ); // why -1?

Serial port read

char chArrBuf [256];
memset (&chArrBuf , '\0', sizeof(chArrBuf) );

int n = read( hSerial, &chArrBuf , sizeof(chArrBuf) );

Serial port close


Recommended includes for this task are: stdio.h, stdlib.h, string.h, unistd.h, fcntl.h, errno.h, termios.h.

courses/be5b99cpl/labs/lab04.txt · Last modified: 2017/10/12 08:44 by faiglj