Non-Interlaced Picture For Electron

Owners of the Acorn Electron home computer may well object to its interlac- ed, and therefore slightly instable, pic- ture. There is a trace of display flicker in non-moving areas on the screen, and this is mainly due to the internal video procesing circuitry operating on the basis of interlacing, a technique used in conventional TV transmission for smoothing the appearance of moving picture areas. Arguably, interlacing is not very useful in computers, since these work with text in most appli- cations. Special displays with a rela- tively long afterglow time are no remedy for this awkward problem, and that is why the present circuit was de- signed. It effectively switches off the in- terlace function, and so ensures a restful display, albeit that the individual lines that make up the characters become slightly more prominent. Figure 1 shows that a TV picture is com- posed of 625 lines divided between 2 rasters of 312.5 lines each. In an inter- laced picture, these rasters are vert...