CTTY is used to change the port for the input device used to give commands to the computer.
If a serial port is to be used for an input device, the baud rate, parity, bits, and stop bit must be established with the MODE-Serial Port Configuration command before using the CTTY command.
Many programs do not use MS-Dos for input or output but send input directly to the hardware on your computer and the CTTY command has no effect on these programs.
As an alternative to the CTTY command, the device parameter of the COMMAND command can be used to specify the input device.
Some batch files have been published in which all output to the screen is prevented by using the CTTY command coupled with the NUL port. This also disables the keyboard. It is therefore imperative to include a line at the end of the batch file returning control to the CON port. If the batch file should quit before the end for any reason, the only way to regain control is to reboot. It is not wise to include such commands in "autoexec.bat"!
To change control of all input and output from the monitor and keyboard to a remote terminal device connected to the AUX port:
To transfer input and output back to the monitor and keyboard, at the remote terminal