GB1101122A - Improvements relating to data transmission systems - Google Patents

Abstract

1,101,122. Electric selective signalling. EVERSHED & VIGNOLES Ltd. 2 April, 1965 [2 April, 1964; 30 July, 1964; 28 Aug., 1964; 9 Dec., 1964], Nos. 13650/64, 30231/64, 35395/64 and 50120/64. Heading G4H. [Also in Divisions G1 and H4] A data communication system uses durationsignificant signals to select transmitters and receivers on a common communication channel. Each transmitter or receiver has a characteristic duration or sequence of durations and responds to reception from a calling pulse generator on a first line of signals having said duration(s) by transmitting or receiving data respectively on a second line. The transmitters and receivers may be selected in any combinations and order, either in a variable sequence, or a fixed sequence repetitively (Fig. 11, not shown). Recognition of a single characteristic duration (Fig. 2).-At a transmitter T the leading edge of a received calling pulse sets a first flip-flop FF1 and actuates a first timer TA which produces an output after a time slightly less than the characteristic duration of the transmitter. This output causes a second timer TB to close an AND gate TG for a period defining a tolerance interval about the end of the characteristic duration. If the calling pulse has not got the appropriate duration to select this transmitter, the trailing edge of the calling pulse will reset the flip-flop FF1 via the gate. Otherwise, the gate TG will be closed at the appropriate time and the flip-flop FF1 will remain set to cause the leading edge of the next calling pulse (whether specific to this transmitter or not) to set a second flip-flop FF2 thus triggering an amplitude-to-duration converter TEC (see below) to convert and transmit an item of data. A receiver R responds to a calling pulse in the same way except that the second flip-flop FF2 of a selected receiver is set by the leading edge of the data pulse rather than a calling pulse, and triggers a duration-to-amplitude converter RDC (see below) to convert the data being received. Amplitude-to-duration converter (Fig. 3, not shown).-An amplitude-significant voltage (-Es) to be converted is applied between one plate of a capacitor (21) and earth, the other plate of the capacitor being connected to the base of a PNP transistor (22) and a constant current drain circuit (25). Triggering of the converter earths the first plate of the capacitor, thereby cutting off the transistor until the current drain circuit can reduce the base potential again sufficiently for it to conduct. Duration-to-amplitude converter (Figs. 4, 5, not shown).-A duration-significant pulse to be converted is applied to one end of a centretapped resistor or other means acting as a comparator (30), the other end of the resistor receiving a feedback duration-significant pulse from an amplitude-to-duration converter (33) (see above) triggered by the leading edge of the input pulse. A capacitor (31) receives a charging pulse determined in duration and polarity by the difference signal from the comparator. The voltage across the capacitor is passed through an amplifier (32) to the converter output and fed back to the input of the amplitude-toduration converter in the feedback loop. Transmitting angular positions.-Two stator voltages of a rotary transformer (biased to be always positive) are converted in turn to duration-significant D.C. pulses when selected by a calling pulse (Fig. 6, not shown) and transmitted to a receiver where they are converted back to amplitude-significant voltages which are debiased and used to energize a secondary rotary transformer to reproduce the angular position (Fig. 7, not shown). Figs. 8, 9 (not shown) show modifications in the receiver utilizing a servo feedback loop with the second transformer. Embodiment with computer (Fig. 12, not shown).-In this embodiment, a control unit, besides generating calling pulses to select transmitters and receivers as above, concurrently addresses a magnetic core store to store data received on the data line in a location characteristic of its source or pass data from this location to the receivers. A/D and D/A converters are provided between the store and data channel. The control unit also controls a switch linking the store with either the converters or a computer. Acquiring addresses.-Fig. 13 (not shown) shows an embodiment for calling aircraft, each aircraft having a characteristic " address " consisting of a set of pulse durations. An aircraft can cause its address to be added to the list of those known to a central control unit incorporating a calling pulse generator. Every so often the control unit sends the various possible durations in turn and the aircraft signals to stop this sequence when it recognises the first duration of its address. The control unit stores this duration as the first part of the address and then sends the sequence of possible durations again, the aircraft indicating which is the same as the second part of its address in the same way as before, and so on. As a modification, the aircraft, on recognizing its first characteristic duration, sends a short indicating pulse to the control unit after the lapse of a time interval which specifies the second part of its address, this time interval being determined by counting.