Linards Ticmanis wrote:
Michael J. Mahon wrote:The Apple II line, with the sole exception of the IIgs, generates NTSC video "directly", by simply outputing a 14.318MHz stream of bits that are either 1 or 0 (with the exception of the blacker-than-black sync, of course). (In the case of hi-res, the 7MHz bit stream can be considered to be a 14MHz stream with each bit repeated.)Of course single 14MHz bits can appear in Hi-Res where there's a transition between the two color palettes. Setting bit 7 of any byte in Hi-Res simply delays the output of the bits of that byte by one DHR pixel width (one-half Hi-Res pixel width). If one byte is delayed and the next isn't, the last pixel of the delayed byte will be only half a standard hi-res pixel wide, which can be used to get a vertical line in non-standard-hires colors. The same can happen at the right edge of the screen (the black border acts like undelayed bytes with a value of zero).
Thanks, Linards, for pointing that out. In fact, it's the cut off "7MHz bits" that result in the non-hi-res colors Mitchell referred to in some cases when the high bit changesor the first or last pixel on a line is cut off by the blanking window, causing a darker color. Note that if one byte is not delayed and the
next is, the "7MHz bit" may be extended by 50%, resulting in a non- standard lighter color. -michael AppleCrate II: An Apple II "blade server"! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."