Standard TTY devices

The behavior of the standard TTY devices is that of a modem controlled port. They require the Data Carrier Detect (DCD) signal to be high before they can operate. When used on a dial-in modem, the ports will wait for DCD before sending out the login prompt.

When these devices are used with a terminal or other locally connected device, you should wire the DCD signal to the remote equipment's Request To Send (RTS) line. When a terminal is then used for log-in, the system generates a prompt when the terminal is powered-on (RTS, and thus DCD is asserted). It also kills the user session if the terminal is powered-off (lowering the signals).