Abstract: A binary data communication system includes a transmitter unit coupled to a receiver unit via a communications link. The transmitter sends a message signal packet to the receiver. The packet includes data arranged according to mixed protocols. The receiver unit includes a program for detecting both protocols, and for converting data from one protocol (or format) into the other format.

Abstract: A method for downloading software includes transmitting only that portion of the program which is to be updated or otherwise changed. In a preferred aspect, a key is also transmitted which must match a key last stored in EEPROM, to permit the download to be effected.

Abstract: After receiving an answer tone from a receiver modem, a sender modem transmits a series of DTMF pulses of predetermined tone, duration, and spacing. If the receiver modem does not verify that the pulses have the correct tone, duration and spacing, it simply hangs up.

Abstract: Upon detection of a trapped passenger in an elevator car, a resident monitoring device initiates communication between the car and a telephone in the building and between the car and a remote monitoring center. Upon detection of the first responsive telephonic communication from either the remote monitoring center or the telephone in the building, voice communication is established therebetween. Upon detection of a second responsive telephonic communication from the second location to respond, voice communication is established between the car and the second location as well so that simultaneous communication may be conducted between the car, the remote monitoring center, and the telephone in the building. A building telephone has a keypad which can be used to select another car for voice communication with a trapped passenger by pressing a selected key. A telephone ring voltage source is provided for alerting building personnel of a trapped passenger.