## RS485 with DTS on Kernel version >= 3.4 If you are using a recent Linux Kernel with device tree enabled you have to specify inside the device tree source the RS485. After that you can open the serial port as a normal RS232 port. This is an example for the /dev/ttyS2 on Aria G25 or Arietta G25 module:

usart3: serial@f8028000 {
	compatible = "atmel,at91sam9260-usart";
	reg = <0xf8028000 0x200>;
	interrupts = <8 4 5>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_usart3 &pinctrl_usart3_rts &pinctrl_usart3_cts >;
	linux,rs485-enabled-at-boot-time;
	rs485-rts-delay = <0 20>;
	status = "okay";
};

The **rs485-rts-delay** parms are in 0.1 mS instead on mS as written on the Kernel doc. ### Python example This example sends a char on the RS485 bus using a [DAISY-10](/DAISY-10) board wired on the __/dev/ttyS2__ serial port. If you are using a Terra board plug the DAISY-10 on D10 connector ([..see the Terra pinout](/pinout_terra)).

import serial,fcntl, struct
 
ser = serial.Serial(
	port='/dev/ttyS2', 
	baudrate=9600, 
	timeout=1,
	parity=serial.PARITY_NONE,
	stopbits=serial.STOPBITS_ONE,
	bytesize=serial.EIGHTBITS
)  
 
fd=ser.fileno()
 
ser.write("0123456789")	# Send some char on the RS485 bus
s = ser.read(1)			# Wait for a char
print s
ser.close()

## RS485 without DTS on Kernel version < 3.4 If you are using an old Kernel Linux without the device tree you have to setup the rs485 hardware mode as illustrated below: ###Python example

import serial,fcntl, struct
 
ser = serial.Serial(
	port='/dev/ttyS2', 
	baudrate=9600, 
	timeout=1,
	parity=serial.PARITY_NONE,
	stopbits=serial.STOPBITS_ONE,
	bytesize=serial.EIGHTBITS
)  
 
fd=ser.fileno()
serial_rs485 = struct.pack('hhhhhhhh', 1, 0, 0, 0, 0, 0, 0, 0)
fcntl.ioctl(fd,0x542F,serial_rs485)
 
 
ser.write("A")		# Send a "A" char to the serial port
s = ser.read(1)         # Wait for a char
print s
ser.close()

###C example

#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"
#include "linux/serial.h"  
 
#define TIOCSRS485 0x542F
 
int main(void) {
	char txBuffer[10];
	char rxBuffer[10];
	int fd;
	struct termios tty_attributes;
	struct serial_rs485 rs485conf;
 
	if ((fd = open("/dev/ttyS2",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);
 
		// Set RS485 mode: 
		rs485conf.flags |= SER_RS485_ENABLED;
		if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
			printf("ioctl error\n");
		}
 
		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;
}