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Browse Prior Art Database

Break Feature for Half Duplex Modem

IP.com Disclosure Number: IPCOM000082676D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Cooper, RJ: AUTHOR

Abstract

In data transmissions between modulator-demodulator (modem) units, over a half-duplex line, it is often desirable to halt transmission from one modem to permit the other modem to transmit urgent messages. Where frequency shift keying signals (FSK) are used to transmit the data, the use of a third frequency sent out by the receiving station over the line to the transmitting station has been used to initiate a transmission break, but requires an oscillator for the different frequency.

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Break Feature for Half Duplex Modem

In data transmissions between modulator-demodulator (modem) units, over a half-duplex line, it is often desirable to halt transmission from one modem to permit the other modem to transmit urgent messages. Where frequency shift keying signals (FSK) are used to transmit the data, the use of a third frequency sent out by the receiving station over the line to the transmitting station has been used to initiate a transmission break, but requires an oscillator for the different frequency.

In the diagram is shown a half-duplex system in which the break feature is implemented without the need for extra oscillators. The transmitting station 1 will be sending out data on a half-duplex transmission line 2 at space frequency Fs or mark frequency Fm to the receiving modem 3, which converts the signals back to output data. When the receiving modem 3 needs to stop modem 1 from further transmissions, it will put its own space frequency Fsr on the line 2.

The transmitter 1 will have a detector unit including a mixer 4 which receives the transmitted frequencies Fs or Fm over a line 5 from the transmitter, and also all of the line frequencies through a transformer 6. The output of mixer 4 will be Fs or Fm, with the possibility of a small 2Fs or 2Fm signal due to distortions, reflections, etc., in the line 2 for so long as modem 3 is not sending out its Fsr. With an Fsr signal on line 2, the output of mixer 4 will be Fs+Fsr or Fm+Fsr plus any dist...