GB1097529A - Data handling system - Google Patents

Abstract

1,097,529. Selective signalling. A. C. NIELSEN CO. Oct. 26th, 1965 [Nov. 12, 1964], No. 45260/65. Heading G4H. In a system for centrally monitoring a plurality of remote T.V. receivers data is transmitted between the central station and the remote stations by means of binary words each bit being represented by a long or a short duration pulse, and each remote station includes a shift register which performs the dual functions of staticising received call words from the central station and dynamicising data indicating the condition of the T.V. receiver(s) at that remote station. The leading edge of each bit received by a remote station is used (after differentiation) to zeroise a free running counter counting clock pulses at 120c/s. derived from the domestic power supply. The counter controls a gate so that if the input pulse is a long pulse (nominally 75 ms.), and therefore exceeds a count of 7 clock-pulses (=58 ms.), the gate opens thereby indicating the receipt of a long pulse. The absence of an output from the gate before the next input pulse is received indicates a short pulse. Calls from the central station comprise an 8-bit word which is preceded by an extra long start pulse (nominally 133 ms.), which is recognized at aremote station by a start pulse gate controlled by the counter to open at a count of 12 (=100 ms). The leading edge of every pulse received by a remote station, in addition to zeroising a counter so that the type of pulse (i.e. short, long or start) can be ascertained, also shifts the contents of a shift register one position and inserts a zero bit into the lowest (i.e. the input) stage. If a received bit is either a long pulse or a start pulse, the long pulse gate eventually opens and inserts a one bit into the lowest stage of the shift register. If a received bit is a start pulse, the start pulse gate eventually opens and readies the remote station to examine the following 8-bit call word to see if it is being called. It also enters zero-bits into every stage of the shift register except the first (which now has a one-bit in it). Thus upon the transmission of a start pulse by the central station the shift register at each remote station has firstly a one-bit inserted into its lowest stage, and secondly all its other stages zeroised. A subsequent 8-bit call word is then shifted into the registers. After the 8-bit call word the transmission line is returned to its normal marked condition by the central station. This appears as an extra long pulse to each remote station, and is treated as such, so that a further one-bit is shifted into the register and the start pulse gate produces an output. However, each remote station having been readied by the true start pulse, the output from the start pulse gate merely causes the received call word to be examined and does not change the contents of the register. Thus effectively every call word is both preceded and followed by an additional one-bit making a total of 10 bits in all. As a check on the number of bits received each shift register has 12 stages, the top three of which should contain 001 for a correctly received call word. Provided the call word has been received correctly, one remote station will respond. Its shift register will be cleared and a one-bit will be sequentially shifted along it so as to sequentially transmit a series of bits representing the condition(s) of the associated T.V. receiver(s).