| 摘要 |
1,088,341. Data transmission systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 20, 1964 [Nov. 21, 1963], No. 47315/64. Heading H4P. An exchange for a digital data system comprises a main store having a storage cell for each incoming and outgoing line, the lines and the cells being scanned in sequence so that data is transferred between the cells and the lines on a bit-by-bit basis. In accordance with routing instructions groups of bits (characters) are transferred from cells corresponding to incoming lines to those corresponding to outgoing lines via auxiliary storage bins and thence to the output lines on a bit-by-bit basis. The lines may carry start-stop data, or synchronous data accompanied by sync. signals, and the data may be at various bit rates. The lines are scanned several times per bit. When the scanning unit scans a given line, a word from the corresponding cells in the main store is passed to a register. In the case of start-stop data this word includes a bit indicating the previous status of that line, i.e. start indicating that a character is being received or stop. If the status bit is a stop bit it is compared with the bit currently on the line being scanned. If they are equal the word is returned to the store, but if unequal, indicating the start of a character, the status bit is reversed, the time of occurrence t is noted and a time indication t + 1À5T stored in the register (T is the bit duration). The content of the register is then returned to store. The next time the line is scanned the status bit is a start bit. The word read from the store is returned to it unless the time of scanning is t + 1À5 T, i.e. the middle of the first data bit, in which case the time indication in the register is incremented by T and the bit state of the line read in to the register. The register content returns to store. When the cycle has repeated often enough for the register to be filled by a received character the character is passed to a bin selected on detection of the start of message sequence by a processor associated with the exchange. On detection of the end of message sequence the complete message in the bin is processed and assigned to an output line bin in accordance with routing instructions. When the output line is scanned, the message is read out to it via the register in an analogous manner. Reception and transmission of synchronous signals is similar but must take account of the acommpanying sync. signals for detection of bits on a line. The system treats the synchronous data in blocks of length dependent on the capacity of the register. |
