GB1157198A - Selective Signalling System - Google Patents

Abstract

1,157,198. Selective calling arrangements. AMP Inc. 10 Nov., 1967 [14 Nov., 1966], No. 51271/67. Heading G4H. One of a number of field stations is called by transmitting a code corresponding to the desired field station, the code being received at the field station and compared bit-by-bit with a locally generated code unique to that station. The signals may be transmitted by radio, a laser beam or a line. At the field station they are applied to a pulse shaper, 114, Fig. 2, to obtain a series of seven square pulses, the first being a start pulse, the next five being the code and the last being an end pulse. The start pulse passes on lead 116 to start a clock oscillator 120 which, through a driver 124, causes a " 1 " bit in the first place of shift register 126 to step through the stages giving successive signals on outputs p, q, r, s, t. In code plug 128, two of these terminals are connected to the corresponding terminals P, Q, R, S, T which are connected, together with the output from the first stage of the shaft register, to Or gate 146. The output y consists of a series of pulses, the start pulse and two of the next five possible pulses, being the station code. This signal is compared in Exclusive-Or gate 122 with the incoming signal x on lead 118. If there is disagreement an output is given by gate 122, which passes over line 144 to reset circuit 136, stopping the oscillator 120 and resetting the shift register to the initial condition. If there is agreement the seventh clock pulse moves the " 1 " bit in shift register 126 into the seventh position to give an output on lead 130. This resets the circuit ready for the next part of the operation and sets flip-flop 152 the output of which restarts the oscillator 120 to cause the code to be read out again from the code plug 128. A switch 155, enabled by flip-flop 152 causes the code y to be transmitted back to the central station to indicate that the selected station has responded. In another embodiment the calling signal consists of 4 decimal digits each represented by five bits, two of which are present.