■DTR Control — For compatibility with IRC, the terminal must assert DTR whenever a communication session is open. IRC uses the DCD control signal (which is driven by the terminal’s DTR output) to determine whether a remote session is open. IRC ignores any serial port activity whenever DCD is inactive. Consequently, if the terminal does not assert it’s DTR output, it is impossible to establish a connection with IRC. Conversely, the terminal must lower DTR whenever a communication is closed. This ensures that the current user is properly logged out and IRC will return to a passive state.
■DCD Interpretation — IRC asserts it’s DTR serial port control signal whenever it is prepared to accept an incoming login request. Through the
