'''Data Terminal Ready''' ('''DTR''') is a [[control signal]] in [[RS-232]] serial communications, transmitted from a data terminal (DTE), such as a computer, to a data communicationscircuit-terminating device (DCE), for example a [[modem]], to indicate that the terminal is ready for communications and the modem may initiate a communications sessionchannel.
The DTR signal is present on pin 20 of the 2522-wire RS-232 interface using a [[DB-25]] connector, and on pin 4 of a newer [[DE-9]] serial port. The signal is asserted (logic ''0'') by raising the voltage of the pin from lownegative to highpositive. Dropping the signal back to its lownegative state indicates to the modem that the communications session shall be terminated.
