Automatic synchronizing system for digital asynchronous communications

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.

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.

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.