Patent GB-1339987-A (GB)
Title: Data collection and transmission system
IPC: H04H1/00
Filed: 1971-04-19
Abstract: 1339987 Selective signalling A C NIELSEN CO 19 April 1971 [2 March 1970] 24332/71 Heading G4H [Also in Division H3] In a data collection and transmission system, records of digital variables are placed in a memory when they fluctuate, and not normally periodically, and the memory contents are transmitted. At a remote unit, 4 TV receivers each present a 5-bit signal indicating the tuner setting and on/off status to a common TV data register (recirculating shift register) the contents of which are continually compared in series with the 20-bit data portion of one of 40 "change lines" in a 1201-bit recirculating shift register memory. Each "change line" is 30 bits of the recirculation loop, consisting of the 20-bit data portion and a 10-bit binary count. The remaining bit of the 1201 bits is a marker bit which is inverted on each circulation. If the comparison shows no change, the count is incremented by one. If the comparison shows a change, the contents of the TV data register are stored in the data portion of the next "change line" with a count of zero, and it is this "change line" which is compared with the TV data register next. The next "change line" is also taken if the count reaches capacity. When a computer at a central unit wishes to receive the contents of the 1201- bit memory, it interrogates (ringing signal only) the remote unit over the telephone network, and the remote unit sends the contents in frequencymodulated form, only every 256th bit being read out on each memory circulation to reduce bit rate. At the central unit, the 1201 bits and the carrier are detected and supplied to a data synchronizing unit communicating via a data interface unit with the computer. Power failure (with switch to back-up battery) at the remote unit is signalled to the computer. Data synchronizing unit.-A clock-driven mod 32 counter produces strobe pulses from its last stage and the phase of these is compared with that of level transition pulses from the 1201-bit stream, in a mod increase circuit and a mod decrease circuit. These two circuits control the first stage of the mod 32 counter to alter its modulus to 33 or 31 as necessary to achieve phase synchronization. When the carrier disappears at the end of a transmission, the mod 32 counter continues to a count of 17 at which it is stopped. When the carrier reappears (in the next transmission), the counter is permitted to continue counting, in synchronism with the first level transition signal. Data. interface unit.-The strobed 1201-bit data stream from the data synchronizing unit is inserted into a 1201-bit shift register, the bits being counted in a mod-1201 counter. The same set of 120 bits is transmitted repeatedly, each set being compared with the current contents of the shift register, any bit inequality resetting the counter. In the absence of transmission error for two successive transmissions, the counter will be reset by the inequality of the marker bits in the two transmissions and will thereafter count without resetting up to 1200 at which a "ready" signal will be produced to interrupt the computer and the shift register caused to recirculate without change. The computer calls for each bit from the register individually at its own speed.