Editing Videotex (section)

===Canada===

Since 1970, researchers at the [[Communications Research Centre]] (CRC) in [[Ottawa]] had been working on a set of "picture description instructions", which encoded graphics commands as a text stream. Graphics were encoded as a series of instructions (graphics primitives) each represented by a single ASCII character. Graphic coordinates were encoded in multiple 6 bit strings of XY coordinate data, flagged to place them in the printable ASCII range so that they could be transmitted with conventional text transmission techniques. ASCII SI/SO characters were used to differentiate the text from graphic portions of a transmitted "page". In 1975, the CRC gave a contract to [[Norpak]] to develop an interactive graphics terminal that could decode the instructions and display them on a colour display, which was successfully up and running by 1977.

Against the background of the developments in Europe, CRC was able to persuade the Canadian government to develop the system into a fully-fledged service. In August 1978, the Canadian [[Department of Communications (Canada)|Department of Communications]] publicly launched it as [[Telidon]], a "second generation" videotex/teletext service, and committed to a four-year development plan to encourage rollout.  Compared to the European systems, Telidon offered real graphics, as opposed to block-mosaic character graphics.  The downside was that it required much more advanced decoders, typically featuring [[Zilog Z80]] or [[Motorola 6809]] processors.