Jeff Blakeney wrote in message news:39bd390c.5995845@24.9.0.17... > > I don't know the exact details of how everything works but I have > never seen a half pixel shift in 80 column or DHR mode. If you can > get a half pixel shift, then it should be possible to write a program > that will display 1120 pixels across the screen (just like you can get > 560 pixels on a regular HR screen). This requires using a monochrome > monitor, though. 1120 pixels? Not possible since all 560 pixels are shifted. There is simply no place to draw any more pixels, not to mention no data to associate with them. Remember, this is a phase shift(a delay in the timing) not a move to new discrete set of 1/2 pixels. Not to mention that the display would have to be driven by at least a 28MHz clock! > The reason you get colour fringes on text in mixed graphics/text mode > is because the colour burst signal is on. Correct. The color burst signal produces timing delays in the pixels that are shifted onto the screen. These shifts are what produces the colors. The 140x192 mode of DHGR fetches it's pixel data from character ROM based on the patterns stored in the data stream. This is why both aux and main memory bytes are fetched simultaneously. This allows 140x192 to use the same color tables that 40x48 uses, and thus produce the same colors. > When you are in text only > mode, the colour burst signal is turned off so you don't see any > colour fringes. However, there is no way to control the colour burst > using software. It is done automatically by the hardware. Also correct. Now here's the fun part. Although the 140x192 is called "double high-resolultion" because it is effectively 140x192x16 where hires is only effectively 140x192x6(or 8) it actually acts more like a Super LoRes because it runs using the same output method as 40x48 lores graphics. When bit 7 of the aux byte in an even column is turned on, the display switches from using the lores display method to using the hires display method. This 560x192 mode acts just like hires with the exception that the PAL unit always receives a 0 for data bit 7 so you can only expect either purple or blue fringes, if any at all. Why only bit 7 from an even byte? This is mostly speculation from the tests I've done but... Since using the lores color data in character ROM requires it to fetch a different pattern depending on the address of the byte(even or odd), the low bit of the address A0 is used to signify which pattern block to fetch the color pattern from. On the way to the block, A0 is used to latch aux bit 7 if A0 is low. The contents of the latch go on to select the lores hardware if the latch bit is low or the hires hardware if the latch bit is high. This is hte only model I can think of that is cheap, fast, and produces the effects I have been seeing on my TV screen. Arkain