On 10 Sep 2000, David Wilson wrote: > Date: 10 Sep 2000 11:24:02 +1100 > From: David Wilson > Newsgroups: comp.sys.apple2, comp.emulators.apple2 > Subject: Re: DHGR Video Riddle Solved!!! > > Matt Jenkins writes: > >In comp.sys.apple2 Jeff Blakeney wrote: > >> By the way, I'm only aware of one DHR mode. 560x192. The number of > >> colours you get depends on whether you view it on a colour or > >> monochrome monitor. If viewed on a colour monitor, you will get 16 > >> colours but if you view it on a monochrome monitor, those 16 colours > >> appear as different dot patterns and you can see all 560 horizontal > >> dots. > > >That's not correct. There is indeed *two* modes of DHR, 560x192 BW and > >140x192 16 color. Whether a byte in the video area is interpreted as > >color pixels or BW pixels is dependant on the high order bit of that byte. > > But only if you have an RGB card. If you use composite video on a //e bit 7 > is ignored in DHR mode. > -- > David Wilson School of IT & CS, Uni of Wollongong, Australia > Hello, (Uh, this is my very first posting to a newsgroup. Please have patience with me and my poor English.) If I understood this thread right, there seems to have been the question whether the high-bit in double-hiresmode influences the output of the screen, either monochrome, colour or something inbetween. To find proof of such a behaviour I've programmed my emulator in such a way that it tells me the value of the high-bit. Then I took a look at some well-known programmes whether they keep the high-bit on or off. Here are my findings: Text = Characters (should typically use monochrome mode for higher resolution) Graphic = Pictures, shapes etc (should typically use coulor mode) BW = black characters on white background WB = white characters on black background Text Graphic Airheart off off Battlechess off off California Games off off Dragon Wars BW on off WB off Maniac Mansion off on every fourth column off(?) Might&Magic 2 off off every fourth column on(?) Neuromancer BW on background on WB off shapes off Pirates on on Rampage on on Testdrive off off three bright columns on the car-select page have the high-bit set. Reason unknown. Transylvania off on Conclusion: As you can see from this table, there doesn't seem to be any evidence of a systematic usage of the high-bit as a switch between different resolutions. Even if it was built into the hardware it was definitely not used by the programmers. 'Neuromancer' and 'Dragon Wars' show that the setting of the high-bit was rather influenced by the character set, not the resolution. In addition, 'Neuromancer', 'Maniac Mansion', 'Might&Magic 2' and especially 'Testdrive' show that programmers even mixed both high-bit on and high-bit off within the same picture but without any relation to the actual content of the picture, only perhaps as a result of some programming algorithm (e.g. shapes). Cheers Holger