CTTY--Notes Setting up a serial port for CTTY Use the MODE command to set up your serial port for baud rate, parity, bits, and stop bit before using the CTTY command. Using CTTY with programs that do not use MS-DOS Many programs do not use MS-DOS for input or output. These programs send input directly to the hardware on your computer. The CTTY command has no effect on these programs; it affects only programs that use MS-DOS for reading keyboard input and displaying output. Setting the terminal device with COMMAND In addition to the CTTY command, you can use the device parameter of the COMMAND command to specify the input device.