GB1484343A - Data transmission - Google Patents

Abstract

1484343 Data transmission; television BRITISH BROADCASTING CORP 6 Aug 1975 [13 Sept 1974] 40086/74 Headings H4P and H4F A ditital data transmission system, e.g. for additional information transmitted during the vertical blanking periods of television signals, comprises a transmitter arranged to transmit data bits serially in alternate bit intervals only and to transmit protection bits in the intervening bit intervals, and a receiver including means for clocking received bits into a shift register at half bit-rate with a phase such that the data bits are clocked into the register and the intervening protection bits are discarded. As shown, a data source 10 supplies bytes of four data bits 2, 4, 6, 8 in parallel and these are entered in a shift register 11. The bits are also applied to an encoding matrix 12 which generates corresponding Hamming code protection bits 1, 3, 5, 7 and these are entered in a second shift register 13. Shift pulses from a divide-by-two stage 16, fed from a bit-rate clock 15, are applied to the registers, whereby the bits are clocked out alternately from the two registers and combined through an OR gate 14 so that the output on line 17 consists of eight bits in the serial order denoted by the numerals 1 to 8. A single 8 bit shift register may replace the two registers 11, 13, and an embodiment with this modification is described with reference to Fig. la (not shown). A suitable receiver is described with reference to Fig. 3 (not shown).