| 摘要 |
The present invention provides method and apparatus for testing data transmissions between fax modems (and other data transmission devices which utilize asynchronous serial ports for connection of DTE equipment) through synchronization and resynchronization of data bits input to a computer from a receiving fax modem with a plurality of preshifted sequences of data bits stored in the computer's memory. In a closed loop testing environment, first and second fax modems are connected together via a synchronous telephone line and are coupled to a computer via first and second asynchronous lines input to the computer's COM ports. The program utilized by the computer initially stores in memory a first sequence of data bits partitioned into units with each unit comprising N data bits. It then stores in memory N-1 preshifted sequences of data bits with each consecutive preshifted sequence comprising data bits corresponding to the data bits of the first sequence successively shifted by one data bit from each preceding preshifted sequence. The data bits of the first sequence are then transmitted to the first modem for retransmission via the FAX CCITT T.4/T.30 standards to the second modem. The computer then receives as output from the second modem an input sequence of data bits which is then synchronized with one of the first and the N-1 preshifted sequences of data bits being designated as a synchronized sequence. If a bit disparity occurs, the input sequence of data bits is resynchronized with one of the first and N-1 preshifted sequences of data bits being designated as a resynchronized sequence. In this manner, the cause of the bit disparity can be determined by calculating a bit shift number corresponding to a number of data bits the resynchronized sequence is shifted from the synchronized sequence.
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