Moxa IA3341-LX [62/72] Baudrate error
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Moxa IA3341-LX [62/72] Baudrate error

Moxa IA3341-LX [62/72] Baudrate error
IA3341 Linux User’s Manual Programmer’s Guide
6-7
2. Function: MOXA_GET_OP_MODE
int ioctl(fd, MOXA_GET_OP_MODE, &mode)
Description
Get the interface mode. Argument 3 mode will return the interface mode.
There are two Moxa private ioctl commands for setting up special baudrates.
Function: MOXA_SET_SPECIAL_BAUD_RATE
Function: MOXA_GET_SPECIAL_BAUD_RATE
If you use this ioctl to set a special baudrate, the termios cflag will be B4000000, in which case the
B4000000 define will be different. If the baudrate you get from termios (or from calling tcgetattr())
is B4000000, you must call ioctl with MOXA_GET_SPECIAL_BAUD_RATE to get the actual
baudrate.
Example to set the baudrate
#include <moxadevice.h>
#include <termios.h>
struct termios term;
int fd, speed;
fd = open(“/dev/ttyM0”, O_RDWR);
tcgetattr(fd, &term);
term.c_cflag &= ~(CBAUD | CBAUDEX);
term.c_cflag |= B4000000;
tcsetattr(fd, TCSANOW, &term);
speed = 500000;
ioctl(fd, MOXA_SET_SPECIAL_BAUD_RATE, &speed);
Example to get the baudrate
#include <moxadevice.h>
#include <termios.h>
struct termios term;
int fd, speed;
fd = open(“/dev/ttyM0”, O_RDWR);
tcgetattr(fd, &term);
if ( (term.c_cflag & (CBAUD|CBAUDEX)) != B4000000 )
{// follow the standard termios baud rate define} else
{ioctl(fd, MOXA_GET_SPECIAL_BAUD_RATE, &speed);}
Baudrate error
Divisor = 921600/Target Baud Rate. (Only Integer part)
ENUM = 8 * (921600/Targer - Divisor) ( Round up or down)
Inaccuracy = (Target Baud Rate – 921600/(Divisor + (ENUM/8))) * 100%
E.g.,
To calculate 500000 bps
Divisor = 1, ENUM = 7,
Error = 1.7%
*The error should less than 2% for reliable data transmission.
Special Note
1. If the target baudrate is not a special baudrate (e.g. 50, 75, 110, 134, 150, 200, 300, 600, 1200,
1800, 2400, 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600), the termios
cflag will be set to the same flag.
2. If you use stty to get the serial information, you will get speed equal to 0.

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