US4225960A
Expired / Lapsed
US
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Automatic synchronizing system for digital asynchronous communications
Assignee: Northrop Grumman Corp
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Filing: 1979-03-01
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Granted: 1980-09-30
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Expires: 1999-03-01
Abstract
Abstract An asynchronous system for transmitting digital data from a data origination station to a data utilization station over a communications path such as an ordinary long-distance telephone network is disclosed. The system includes circuitry for synchronizing and maintaining synchronization between the receiving circuits and the transmitting circuits and for correcting errors introduced by the communications path. Each data word transmitted has associated therewith a synchronization code comprising a stop bit and a start bit. During normal operation, the system is synchronized by detecting the start bit which precedes the information portion of each data word. Synchronization is maintained for several data words even though the start bit is not detected due to interference, for example, by an auto-synchronization signal which includes a pulse positioned within the time period during which the start bit would normally be detected. Additionally, should a predetermined number of successive data words arrive at the receiver with errors, the auto-synchronization signal is disabled based on the assumption that the errors are due to a loss of synchronization. The transmitter circuits then transmits two synchronizing words, each containing the synchronization code with all other bits having a logic "zero" level. The synchronization code of the two synchronizing words resynchronizes the system thereby restoring normal operation. That is, the system maintains normal synchronization even though interference destroys the start and/or stop bits of a number of successive words. Should this interference continue such that the automatic synchronization circuits can no longer maintain synchronization, the auto synchronization circuit is disabled and normal synchronization is restored by transmitting two special synchronization words, all without any loss of data.
Inventors
- 👤 Harvey M. Masters
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 17:35
CPC Classifications
H; H04; H04L; H04L1/00; H04L1/12; H04L1/14; H04L7/00; H04L7/0079; H04L7/0083; H04L7/04; H04L7/041; H04L7/044
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
458 words
A data transmission system including a data origination and a data utilization station and means for maintaining synchronization therebetween when detection of synchronizing codes used in synchronizing said data origination station with said data utilization station is interrupted: (1) said data origination station comprising; (a) means for selectively and sequentially accepting digital data from a data source and for transmitting said digital data as a plurality of data words each including a synchronizing code, a field code and a data portion, as a continuous output data stream, (b) means for temporarily storing a selected number of said data words comprising said output data stream; (c) means for receiving a return data stream comprising a plurality of data words from said data utilization station, (d) means for detecting the synchronizing code of each data word comprising said return data stream to generate a pulsed synchronizing signal; (e) means for generating an auto synchronization signal including a pulse substantially coincident with said synchronizing signal; (f) means for combining said pulsed synchronization signal with said auto synchronization signal to generate an initiate signal; (g) means responsive to said initiate signal to produce a multipulse clock signal which shifts the data words comprising said returned data stream into a shift register; (h) means for selectively comparing data words comprising said returned data stream to said stored data words to generate a compare signal; (i) means responsive to said compare signal to generate a loss of synchronization signal whenever a predetermined successive number of comparisons indicate that the selected word of said returned path stream is not identical to the word to which it is being compared; (j) means responsive to said loss of synchronization signal to interrupt said output data stream and insert therein at least one synchronization word, said synchronizing word having all bits the same value except for said synchronization code; (2) said data utilization station comprising; (a) means for detecting said synchronization code of each of said data words comprising said output data stream to generate a pulsed synchronization signal, (b) means for generating an auto synchronization signal including a pulse substantially coincident with said synchronizing signal, (c) means for combining said pulsed synchronization signal and said auto synchronization signal to generate an initiate signal, (d) means responsive to said initiate signal to shift a selected number of the data words comprising said output data stream into a memory and for generating said returned data stream, (e) means responsive to said field code of each of said data words to generate a loss of synchronization signal, (f) means responsive to said loss of synchronization signal to disable said means for generating an auto synchronization signal and for resynchronizing said data utilization station with said data origination station synchronizing word.
Claim 2
Dependent Claim
458 words
A data transmission system including a data origination and a data utilization station and means for maintaining synchronization therebetween when detection of synchronizing codes used in synchronizing said data origination station with said data utilization station is interrupted: (1) said data origination station comprising; (a) means for selectively and sequentially accepting digital data from a data source and for transmitting said digital data as a plurality of data words each including a synchronizing code, a field code and a data portion, as a continuous output data stream, (b) means for temporarily storing a selected number of said data words comprising said output data stream; (c) means for receiving a return data stream comprising a plurality of data words from said data utilization station, (d) means for detecting the synchronizing code of each data word comprising said return data stream to generate a pulsed synchronizing signal; (e) means for generating an auto synchronization signal including a pulse substantially coincident with said synchronizing signal; (f) means for combining said pulsed synchronization signal with said auto synchronization signal to generate an initiate signal; (g) means responsive to said initiate signal to produce a multipulse clock signal which shifts the data words comprising said returned data stream into a shift register; (h) means for selectively comparing data words comprising said returned data stream to said stored data words to generate a compare signal; (i) means responsive to said compare signal to generate a loss of synchronization signal whenever a predetermined successive number of comparisons indicate that the selected word of said returned path stream is not identical to the word to which it is being compared; (j) means responsive to said loss of synchronization signal to interrupt said output data stream and insert therein at least one synchronization word, said synchronizing word having all bits the same value except for said synchronization code; (2) said data utilization station comprising; (a) means for detecting said synchronization code of each of said data words comprising said output data stream to generate a pulsed synchronization signal, (b) means for generating an auto synchronization signal including a pulse substantially coincident with said synchronizing signal, (c) means for combining said pulsed synchronization signal and said auto synchronization signal to generate an initiate signal, (d) means responsive to said initiate signal to shift a selected number of the data words comprising said output data stream into a memory and for generating said returned data stream, (e) means responsive to said field code of each of said data words to generate a loss of synchronization signal, (f) means responsive to said loss of synchronization signal to disable said means for generating an auto synchronization signal and for resynchronizing said data utilization station with said data origination station synchronizing word.
Claim 3
Dependent Claim
34 words
A data transmission system in accordance with claim 1 wherein said field codes are indicative of the original sequence in which digital data comprising said digital data words was accepted from said data source.
Claim 4
Dependent Claim
42 words
A data transmission system in accordance with claim 2 wherein said data utilization station includes means for examining the sequence of the field codes associated with the arriving data words and for determining if said field codes arrive in the expected sequence.
Claim 5
Dependent Claim
48 words
A data transmission system in accordance with claim 3 wherein said data utilization station further includes means for selectively reading data words stored in said memory and for coupling these digital data words to a data sink in response to the expected sequence of subsequently arriving field codes.
Claim 6
Dependent Claim
57 words
A data transmission system in accordance with claim 4 further including circuitry for generating a loss of synchronization signal whenever a preselected number of data words comprising said output data stream have arrived at said data utilization station without any of said digital data words having been read from said memory and coupled to said data sink.
Claim 7
Dependent Claim
163 words
A data system comprising: (1) a data origination station including, (a) means for combining a synchronizing code with digital data to be transmitted from a data origination station to a data utilization station; (b) means for detecting a loss of synchronization and for generating a loss of synchronization signal; (c) means for interrupting the transmission of data in response to said loss of synchronization signal and for transmitting at least one synchronizing word in which all bits except a synchronization code have the same logic level; (2) said data utilization station including, (a) means for detecting said synchronization code associated with each of the data words to synchronize said data utilization station with said data origination station; (b) means for detecting loss of synchronization and for generating a loss of synchronization signal; (c) means responsive to said loss of synchronization signal and to said at least one synchronizing word and in response thereto re-establishing synchronization between said data origination and data utilization stations.
Claim 8
Dependent Claim
163 words
A data system comprising: (1) a data origination station including, (a) means for combining a synchronizing code with digital data to be transmitted from a data origination station to a data utilization station; (b) means for detecting a loss of synchronization and for generating a loss of synchronization signal; (c) means for interrupting the transmission of data in response to said loss of synchronization signal and for transmitting at least one synchronizing word in which all bits except a synchronization code have the same logic level; (2) said data utilization station including, (a) means for detecting said synchronization code associated with each of the data words to synchronize said data utilization station with said data origination station; (b) means for detecting loss of synchronization and for generating a loss of synchronization signal; (c) means responsive to said loss of synchronization signal and to said at least one synchronizing word and in response thereto re-establishing synchronization between said data origination and data utilization stations.
Claim 9
Dependent Claim
162 words
A circuit for maintaining a receiving circuit of an asynchronous digital data system synchronized with a transmitting circuit of said system, comprising: (a) means for detecting a start bit preceding the data portion of each data word transmitted by said transmitting circuit to generate a pulsed synchronizing signal; (b) timing signal generating means responsive to said pulsed synchronizing signal to generate timing signals including a clock signal having a pulse positioned in time to shift each bit of each data word transmitted by said transmitting circuit into a shift register; (c) means for detecting the last pulse of said clock signal to generate an auto synchronization signal with the pulses of said auto synchronization signal being substantially coincident with the pulses of said pulsed synchronizing signal; and (d) means for coupling said auto synchronization signal to said timing signal generating means such that said timing signal generating means is initiated by said auto synchronization signal when said pulsed synchronizing signal is interrupted.
Claim 10
Dependent Claim
162 words
A circuit for maintaining a receiving circuit of an asynchronous digital data system synchronized with a transmitting circuit of said system, comprising: (a) means for detecting a start bit preceding the data portion of each data word transmitted by said transmitting circuit to generate a pulsed synchronizing signal; (b) timing signal generating means responsive to said pulsed synchronizing signal to generate timing signals including a clock signal having a pulse positioned in time to shift each bit of each data word transmitted by said transmitting circuit into a shift register; (c) means for detecting the last pulse of said clock signal to generate an auto synchronization signal with the pulses of said auto synchronization signal being substantially coincident with the pulses of said pulsed synchronizing signal; and (d) means for coupling said auto synchronization signal to said timing signal generating means such that said timing signal generating means is initiated by said auto synchronization signal when said pulsed synchronizing signal is interrupted.
Claim 11
Dependent Claim
282 words
An asynchronous digital data transmission system comprising a data origination station and a data utilization station, said data origination station including automatic synchronization circuitry comprising means for detecting loss of synchronization and means for re-establishing synchronization: (1) said means for detecting a loss of synchronization comprising; (a) means for comparing data words of a data stream returned from said data utilization station to data words stored at said data origination station to determine if the stored digital data word to which a word of said data stream returned from said data utilization is compared was correctly transmitted from said data origination station to said data utilization station; (b) counter means including a digital counter which is incremented one count when a word of said data stream returned from said data utilization station is not identical to the digital word to which it is compared and for resetting said counter to zero each time a word of said data stream returned from said data utilization station is found to be identical to the data word to which it is compared; (c) means responsive to the digital number stored in said digital counter to generate a loss of synchronization signal when said number equals a preselected value; (2) said means for re-establishing synchronization comprising; (a) means responsive to said loss of synchronization signal to transmit at least one synchronization word to said data utilization station, (b) means for resuming the normal transmission of data following the transmission of said synchronizing word; and (c) means for comparing a word of said data stream returned from said data utilization station to a word stored at said data origination station to determine if synchronization has been re-established.
Claim 12
Dependent Claim
282 words
An asynchronous digital data transmission system comprising a data origination station and a data utilization station, said data origination station including automatic synchronization circuitry comprising means for detecting loss of synchronization and means for re-establishing synchronization: (1) said means for detecting a loss of synchronization comprising; (a) means for comparing data words of a data stream returned from said data utilization station to data words stored at said data origination station to determine if the stored digital data word to which a word of said data stream returned from said data utilization is compared was correctly transmitted from said data origination station to said data utilization station; (b) counter means including a digital counter which is incremented one count when a word of said data stream returned from said data utilization station is not identical to the digital word to which it is compared and for resetting said counter to zero each time a word of said data stream returned from said data utilization station is found to be identical to the data word to which it is compared; (c) means responsive to the digital number stored in said digital counter to generate a loss of synchronization signal when said number equals a preselected value; (2) said means for re-establishing synchronization comprising; (a) means responsive to said loss of synchronization signal to transmit at least one synchronization word to said data utilization station, (b) means for resuming the normal transmission of data following the transmission of said synchronizing word; and (c) means for comparing a word of said data stream returned from said data utilization station to a word stored at said data origination station to determine if synchronization has been re-established.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-09-30 | 1984-03-31 | 1984-09-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-09-30 | 1988-03-31 | 1988-09-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-09-30 | 1992-03-31 | 1992-09-30 | $7700.00 | Window Closed / Lapsed |