DEWAR.ACF2@NYU-CMCL1.ARPA (12/02/83)
From: Robert Dewar <DEWAR.ACF2@NYU-CMCL1.ARPA> Here are some notes on Compaq video compatibility which may be of interest: The Compaq video interface is a very interesting combination of the color graphics and monochrome interfaces of the IBM PC. It actually switches display modes dynamically (those with sufficiently acute hearing will be able to notice the distinct change in the high pitched tone as the display rate changes). To the eye, the monochrome mode is extremely similar to the IBM display. The color/graphics mode simulates color using grey scales (works fine with Apple Panic, but J-Bird is a problem!). The board also generates RGB and composite video output. I recommend getting a composite monitor (the Panasonic CT1300D about $320 from discount houses is an excellent choice) if you want spiffy color for games (note that for many purposes, composite video gives better color than RGB and you have the fine resolution needed on the Compaq monitor, an ideal combination for the MS flight simulator). To a program, the interface looks just like the color graphics interface (i.e. in either mode the display buffer is at B8000). This works fine for most normal software, since the display will switch into the appropriate mode automatically. However, some software is written to work quite differently in graphics and monochrome mode, and will get confused in the COMPAQ environment. For example, my DVED screen editor is very careful to respect the annoying retrace restrictions of the color graphics card, while still retaining decent performance. It works OK on the COMPAQ, but there are cases when it is less efficient than it should be, and also it flickers the screen unnecessarily (the COMPAQ monochrome mode does not require the program to bother about retrace restrictions). I eventually added a test for the COMPAQ copyright notice and improved the COMPAQ performance.