prindle@NADC.ARPA (Frank Prindle) (08/29/88)
This weekend I discovered a curious difference between the C128 in C64 mode and the C64 itself: they output slightly different colors to the composite (i.e. 40 column) screen. The major effect is that the C64 (6567 VIC chip) puts out only 5 distinct gray levels (black, white, and three other levels of luminance), while the C128 in C64 mode (8564 VIC chip) puts out 9 distinct gray levels (black, white, and 7 other levels of luminance). Here's the breakdown, in no particular order: C128: C64: Blk Blk Wht Wht Red/DGry Red/DGry/Blu/Brn Blu/Brn Cyn/LGry Cyn/LGry/Yel/LGrn Yel/LGrn Pur/Orng Pur/Orng/Grn/LRed/MGry/LBlu Grn/LRed MGry/LBlu The upshot of this involves commercial software supposedly written to be compatible with a monochrome monitor. One such program I recently purchased is "Glass Tracks" by Sonus (a MIDI sequencer). The display is largely monochrome, but certain selections are highlighted in light green over a light gray background. When used on my C128 in C64 mode with a monochrome monitor, these selections are quite visible; but on the C64 with a monochrome monitor, the highlights cannot be seen! Since Sonus claims their software is monochrome compatible, they probably selected the light green highlight color based on the C128 monochrome capability, but never tested it on a real C64. The addition of gray levels to the 8564 chip is apparently an enhancement that Commodore added to improve performance with monochrome monitors, but developers should be aware that what may work well on the 128 may fail miserably on the 64 in this respect. By the way, in all other respects, Glass Tracks works flawlessly and is an excellent piece of software. Someday, when I find the highlight color in the machine code, I'll just change it (probably to white). Sincerely, Frank Prindle Prindle@NADC.arpa