GB1536532A - Data transmission system - Google Patents

Abstract

1536532 Selective signalling TELEVISION SYSTEMS & RESEARCH Ltd 17 Nov 1975 [15 Aug 1974] 36064/74 Heading G4H In a data transmission system having a computer and a plurality of controllers, the computer is arranged to address the controllers in turn in a "scan" sequence, and address a plurality of addressable elements, associated with an addressed controller, in turn in an "exchange" sequence. In a hotel, the computer is connected by a plurality of links to respective groups of controllers, one controller per hotel room (or controllers may be shared between rooms). Each link has two lines for carrying two-parallel-bit coded signals from the computer to the controllers and a line for carrying indication bits back. The addressable elements associated with a controller in a hotel room comprise three groups viz.: (a) switches whereby the computer controls a morning call buzzer, a lamp indicating a message has been received for the guest and defrosting of a refrigerator, (b) switches to permit the computer to detect use of guest key and staff key to open the refrigerator door, whether this door is open, use of a maid jack plug and a housekeeper jack plug, switching off (by the guest) of the morning call buzzer, and selection (by guest) of TV channels on which the hotel may show films, a "data present" signal being produced when any of these switches (apart from those regarding TV channels) is operated, (c) switches indicating removal of drinks (bottles) from individual compartments of the refrigerator, mechanical means preventing replacement of bottles until the staff key is used. The "exchange" sequence may operate in any of the following modes: (1) with respect to the currently-addressed room only if the computer has control commands for group (a) or the "data present" signal from group (b) is on, (ii) addressing groups (a) and (b), (iii) addressing all groups. Normally, the controllers are scanned continuously and exchange mode (i) is used for each room, but mode (ii) is used every minute and mode (iii) when an instruction arrives from a terminal that group (c) must be addressed for billing or inventory purposes. Addressing of the controllers is by incrementing address counters therein, each controller's counter producing an enabling output on a respective count. Addressing of switches within a thus-selected controller is by incrementing a pair of series-connected counters which perform coordinate selection of a notional matrix of the switches, each in series with a respective diode. The two-parallelbit coded signals from the computer are decoded to increment the appropriate counter(s), change from "scan" sequence to "exchange" sequence and back and supply 0 and 1 control bits for group (a). There is a flip-flop for each of the controlled switches of group (a), and also a test flip-flop, and the two inputs of each flip-flop are addressed in turn from one of the pair of series-connected counters mentioned. The test flip-flop is repeatedly set and reset by the computer which then compares its state with what it should be. Reception, cashier, housekeeper and porter terminals are provided to the computer. Each controller has a power-on circuit to set flip-flops into standard states at power turn-on. In a modification, the three lines per link are replaced by respective frequencies (on-off modulated) on a common line, the frequencies being obtained by dividing- down the output of a common oscillator at the computer end of the system (the frequency used for signalling from controllers to computer being divided down at the controllers from the oscillator output which is supplied unchanged to them for this purpose. Food as well as drinks could be dispensed, and central heating could be controlled separately in each room. Sockets may be provided at the controllers for calling service personnel, e.g. plumber, electrician. The computer may prevent opening of a refrigerator using the guest key. The invention may also be applied to the control of the stocking of drugs in a hospital.