Browse Prior Art Database

Multifrequency Tone Data Transmission

IP.com Disclosure Number: IPCOM000077346D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Donnan, RA: AUTHOR [+2]

Abstract

United States Patent 3,582,895, issued June 1, 1971, discloses two multifrequency tone data transmission techniques. Both techniques utilize the four conventional A and B frequencies only. One technique is capable of generating sixty-four unique codes, by generating a single A frequency and switching the B frequency halfway through the signalling period to some other value, which may include the original B frequency. The sixteen combinations defined by the A and first B frequency are multiplied by the four B frequencies available during the second half, to uniquely define sixty-four characters. The other technique disclosed contemplates switching both the A and B frequencies halfway through the signalling period; thus, providing (16 x 16 = 256) unique tone combinations.

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Multifrequency Tone Data Transmission

United States Patent 3,582,895, issued June 1, 1971, discloses two multifrequency tone data transmission techniques. Both techniques utilize the four conventional A and B frequencies only. One technique is capable of generating sixty-four unique codes, by generating a single A frequency and switching the B frequency halfway through the signalling period to some other value, which may include the original B frequency. The sixteen combinations defined by the A and first B frequency are multiplied by the four B frequencies available during the second half, to uniquely define sixty-four characters. The other technique disclosed contemplates switching both the A and B frequencies halfway through the signalling period; thus, providing (16 x 16 = 256) unique tone combinations.

In those instances where the second half of the signalling element is identical to the first half of a subsequent signalling element, a rest period containing no signal must be provided to detect the new character being signalled. The rest periods reduce data throughput and complicate equipment design to overcome key rolling in key entry devices.

In those instances where a smaller character set will suffice, multifrequency tone pairs may be transmitted without the rest period by selecting only those codes within the set, in which the first half of the signalling element does not occur in the second half of the signalling element. For example, A1-4 and B4 may b...