Table 1: POSIX functions will work on the iPAQ as well as they do on the desktop. The most common of these functions for writing to a serial port are shown here

Function	Parameters	Description
open	char*: serial port name (i.e., "/dev/ttyS0") int: access flags (i.e., O_WRONLY); see bits/fcntl.h	Opens the serial port and returns a handle to it or -1 on error.
close	int: handle to the serial port (obtained by calling open)	Closes the serial port.
tcgetattr	int: handle to the serial port struct termios*: structure containing serial port parameters; see bits/termios.h	Gets the parameters for the serial port and stores them in the given termios structure.
tcsetattr	int: handle to the serial port int: specifies when the changes should take effect (almost always TCSANOW); see bits/termios.h struct termios*: structure containing serial port parameters	Sets the parameters for the serial port. This is typically used to set the baud rate.
cfsetospeed	struct termios*: structure containing serial port parameters speed_t: a constant such as B2400, B9600, etc.; see bits/termios.h	A convenience function to set the output speed of the serial port. The given termios structure must then be set using tcsetattr.
write	int: handle to the serial port void*: buffer containing bytes to be written int: number of bytes in the buffer	Sends the given bytes through the serial port; returns -1 on error.