FOX Board G20 has 7 asynchronous serial interfaces identified in Linux with the device name from /dev/ttyS0 to /dev/ttyS6.

The picture below illustrates where the transmit and receive lines are located:

This port is reserved by default as Linux system console port and is available on the Debug Port pin strip (see DPI product description).

This is the only port where all the handshaking signals requested by a modem link are available.

The RXD and TXD signals of this port are available both on J7 and J16 terminal. J16 is the terminal to weld a connector compatible with (4D systems oLed displays).

To quickly test the serial ports it's installed by default the terminal emulator utility Minicom. Run it from the shell promp typing:

# mincom -s

-s parm runs minicom in setup mode.

Select Serial port setup and type <enter>:

Now type <A> to change the serial port and <F> to disable the hardware flow control. Select Exit from the configuration menu. Now each character press on your keyboard is sent to the selected port and each character received from the serial port is print on the screen.

Type <CTRL-A> and <Z> for more help on Minicom.

This is a basic example on how to use a serial port in Pyhon using the pySerial module (http://pyserial.sourceforge.net/index.html):

import serial
 
ser = serial.Serial(
	port='/dev/ttyS1', 
	baudrate=9600, 
	timeout=1,
	parity=serial.PARITY_NONE,
	stopbits=serial.STOPBITS_ONE,
	bytesize=serial.EIGHTBITS
)  
 
ser.write("A")		# Send a "A" char to the serial port
s = ser.read(1)         # Wait for a char
print s
ser.close()

This is a basic example on how to use a serial port in C.

Refer to these links to understand how it works.

• http://linux.about.com/library/cmd/blcmdl3_termios.htm
• http://www.gnu.org/software/libc/manual/html_node/Low_002dLevel-I_002fO.html#Low_002dLevel-I_002fO

#include <stdio.h>     
#include <string.h>    
#include <unistd.h>    
#include <fcntl.h>     
#include <errno.h>     
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdarg.h>
#include <termios.h>
 
int main(void) {
	char txBuffer[10];
	char rxBuffer[10];
	int fd;
	struct termios tty_attributes;
 
	if ((fd = open("/dev/ttyS1",O_RDWR|O_NOCTTY|O_NONBLOCK))<0) {
		fprintf (stderr,"Open error on %s\n", strerror(errno));
		exit(EXIT_FAILURE);
	} else {
		tcgetattr(fd,&tty_attributes);
 
		// c_cflag
		// Enable receiver
		tty_attributes.c_cflag |= CREAD;		
 
		// 8 data bit
		tty_attributes.c_cflag |= CS8;			
 
		// c_iflag
		// Ignore framing errors and parity errors. 
		tty_attributes.c_iflag |= IGNPAR;		
 
		// c_lflag
		// DISABLE canonical mode.
		// Disables the special characters EOF, EOL, EOL2, 
		// ERASE, KILL, LNEXT, REPRINT, STATUS, and WERASE, and buffers by lines.
 
		// DISABLE this: Echo input characters.
		tty_attributes.c_lflag &= ~(ICANON); 	 
 
		tty_attributes.c_lflag &= ~(ECHO);		
 
		// DISABLE this: If ICANON is also set, the ERASE character erases the preceding input 	
		// character, and WERASE erases the preceding word.
		tty_attributes.c_lflag &= ~(ECHOE);		
 
		// DISABLE this: When any of the characters INTR, QUIT, SUSP, or DSUSP are received, generate the corresponding signal.	
		tty_attributes.c_lflag &= ~(ISIG);		
 
		// Minimum number of characters for non-canonical read.
		tty_attributes.c_cc[VMIN]=1;			
 
		// Timeout in deciseconds for non-canonical read.
		tty_attributes.c_cc[VTIME]=0;			
 
		// Set the baud rate
		cfsetospeed(&tty_attributes,B9600);		
		cfsetispeed(&tty_attributes,B9600);
 
		tcsetattr(fd, TCSANOW, &tty_attributes);
 
		txBuffer[0]='A';
		write(fd,txBuffer,1);
 
		// Read a char
		if (read(fd,&rxBuffer,1)==1) {
			printf("%c",rxBuffer[0]);
			printf("\n");
		}	
	}	
 
	close(fd);	
	return EXIT_SUCCESS;
}