Abstract: Method and apparatus for effecting mode switching from a transmission mode to a command mode of an intelligent modem operatively coupled to a digital data device and a telephone line is disclosed. A termination of the modem's transmission mode is effected after a predetermined silent time interval in which no data is received from the device and prior to the transmission of additional data on the line. Operation of the modem switches to a buffer mode in which data sent from the device is temporarily stored instead of being transmitted on the telephone line. If the stored data is a proper escape sequence, operation of the modem switches to the command mode. If a proper escape sequence is not received, operation of the modem switches to a purge mode in which the stored data is transmitted on the telephone line. The apparatus comprises a data interface, a novel modem controller and a modem engine.