mdj wrote:
On Nov 13, 10:19 am, "Michael J. Mahon" <mjma...@aol.com> wrote:Michael J. Mahon wrote:Bill Garber wrote:"Jerry" <awande...@yahoo.ca> wrote in message m363mt5zna.fsf@yahoo.ca">news:m363mt5zna.fsf@yahoo.ca...mojoehand <jg...@zianet.com> writes:Jerry Penner, I wanted to thank you for the information you emailed, but my reply bounced. It seems that Yahoo is being too agressive in its spam filtering.Must be. There was no message in my spam folder at all, which is the usual case. I would have put the patent document online, but I don't have a web-site right now. For others who are interested, the patent is US# 4,631,692, and can be found at uspto.gov.I went there, and searched it, and the only info available was that it had expired on December 23, 1998. I couldn't actually find the Patent there.Go to: http://patft.uspto.gov/ and select Patent Number Search, then enter 4631692 and you'll see the patent. It describes a 4-bit shift register implementation, where the shift register is clocked at 14.3MHz--the classic 16-color implementation.I see Jerry made an equivalent suggestion. ;-) From the patent description, it seems that AN3 and /80COL need to be made available to the card to do mode selection. (I wonder why the /DEVSEL space wasn't used for this function?)The 80COL and AN3 softswitches are used in the IIe to enable Double Hires and Lores modes. The Video7 RGB adapters established a protocol for toggling these switches in certain sequences which enable selection between DHR colour, mono, mixed, and '160' modes. There's also a FG/BG mode that lets you do 280x192 single hires, and the AUX page holds the FG/BG colours for each screen byte. Using the protocol allows software to 'support' RGB cards by selecting whatever mode is appropriate with completely benign results on non-RGB equipped Apple II's.
Ah, yes--"backward compatibility" for the new software, and simpler than providing a scheme for software to detect the card's presence (or absence). Just what I would have done in the circumstance. ;-) -michael ******** Note new website URL ******** NadaNet and AppleCrate II for Apple II parallel computing! Home page: http://home.comcast.net/~mjmahon/ "The wastebasket is our most important design tool--and it's seriously underused."