| 摘要 |
1,066,909. Data transmission systems; automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 2, 1965, No. 46285/65. Headings H4P and H4K. In a data transmission system the 1 and 0 bits of a character are sent as frequencies f1 and f 2 and are spaced by an interbit frequency f 0 . Preceding and following the character there is sent a signal of frequency f0 lasting for the duration of two bits. Voice frequencies are used, and communication is between the registers of two exchanges. At the transmitter, Fig. 1 (not shown), when data is to be sent a flip-flop (M1) generates an 8 m.sec. signal causing an oscillator to transmit f0. A multivibrator (MV1) now generates a clock train used to read a 4-bit character from a shift register (SR1) and to gate the data read out to the oscillator, thereby producing f1 or f2 followed by f0 as appropriate for each bit. When the register (SR1) is empty the 8 m.sec. flip-flop is again energized to produce the intercharacter frequency f0. At the receiver, Fig. 2 (not shown), frequency selective circuits direct the data to three channels. Those corresponding to f1 and f2 feed a toggle (B2) connected to the input of a shift register (SR2), and that corresponding to f0 to an integrator. If the frequency f0 lasts longer than 5 m.sec. the register content is read out and decoded. Modification.-By transmitting an extra 1 bit at the beginning of a character the need for the integrator at the receiver is removed, since when that 1 bit reaches the last stage of the register read-out is immediately effected. |
