Interix supports access to serial ports. The names for the serial ports are located under /dev. They have the form tty##, where ## is 0 or 1 followed by a hexadecimal number. You can access up to 32 serials ports, from /dev/tty00 through /dev/tty1f, which map to Windows COM ports COM1 through COM32.
For example, the virtual device /dev/tty00 corresponds to port COM1, /dev/tty01 corresponds to COM2, /dev/tty02 corresponds to COM3, and so on.
You can use the Interix igetty(1) utility to configure a serial port for communications.