Abstract: An arrangement for the control of viewing of a television program in which a classification code is transmitted with the video signal, for example, in an extension packet of a teletext signal, includes a decoder (23) which detects the received codes and passes them to a microcontroller (27). An authorized user is able to enter codes of permitted program classifications by means of a remote control unit (28). Codes representing these permitted classifications are stored in a non-volatile memory (29). The received and permitted codes are compared in the microcontroller (27) which inhibits the video (25) and/or audio (32) circuits if the received codes are not permitted codes. The non-volatile memory (29) is arranged to store a plurality of different program classifications, each of which is valid for different periods of the day.

Abstract: A television receiver includes a teletext decoder having a page memory (PM) into which teletext data is read from a data acquisition circuit (DAC) via an interface circuit (MIC) under control of a microprocessor (PRO). The microprocessor is also used to control functions of the television receiver and to cause on-screen display messages to be produced. When an on-screen display message is to be produced, the microprocessor sets a bit in the memory PM which causes a latch to be set which in turn causes a multiplexer (MUX) to apply data from an auxiliary memory (APM) to a character generator (CG). When the on-screen display message is to be deleted, the bit in the page memory is reset causing the latch to be reset and the multiplexer to apply data from the page memory to the character generator. This enables on-screen display messages to be applied to the character generator without losing any of the teletext data stored in the page memory.

Abstract: A teletext decoder arrangement comprises a page memory (PM) operable under the control of a data acquisition circuit (DAC) for storing a teletext page to be displayed, and a background memory (BM) in which teletext data packets are stored in the order in which they are received, a scanning circuit (SC) being provided which, when a teletext page is requested, causes the data packets in the background memory (BM) to be scanned in the B reverse order to that in which they were received to locate the most recently received version of the required teletext page, and to cause the data packets of the required page to be output to the data acquisition circuit (DAC) in the order in which they were received for storage in the page memory (PM) and subsequent display.

Abstract: A decoder for Hamming encoded data in the form of a serial bit stream successive blocks of which are Hamming encoded comprises a serial-to-parallel converter for converting each of the blocks into a plurality of successive parallel bytes, a plurality of parity check circuits for carrying out successive partial parity checks on each of the bytes of a block as each byte is received, and a further plurality of parity check circuits for carrying out parity checks on at least part of successive ones of the bytes as they are received, a parity checker decoder being provided to which the outputs of the parity check circuits are applied for affording an output indicative of possible errors in the block.

Abstract: A teletext decoder is provided with a page memory having rows (R0 to R73) for storing corresponding packets of teletext data, the page memory being provided with at least one extra memory bit (F1, F2) for each row thereof, the extra memory bits constituting flags (F1, F2) which may be selectively set by the processor software in order to initiate selective action in respect of those packets which correspond to the flagged rows. The selective action might be to permit or prevent packets being written into memory or to alert the processor that immediate processing of a flagged packet is required.