Rules for Defining Logical Attributes under PCDOS and OS/2

Remember the following rules when defining logical attributes.

LIGHT and BLINK are not supported as background colors.

If high-intensity background colors are enabled, LIGHT is available for background colors and BLINK is not available for foreground colors.

Avoid UNDERLINE in system logical attributes.

UNDERLINE is not supported by either the Color Graphics Adapter (CGA) or the Enhanced Graphics Adapter (EGA) (except when emulating the MDA).

If you use UNDERLINE in the definitions of the monochrome physical attribute for a system logical attribute, the attribute will not be properly translated in the black and white modes (0 and 2) on either color adapter.

Take into account the differences between the EGA and CGA.

The is the original color adapter supplied by IBM. The was introduced in 1984. The EGA provides compatibility with the CGA. Programs built to run on the CGA will run identically on the EGA.

One important difference between the two adapters is that the EGA can write output to the screen at any point during the video cycle without causing "snow," whereas this cannot be done on the CGA. Vermont Views detects the presence of the EGA and takes advantage of its faster screen output capability.

There are major differences between the CGA and EGA text modes. For example, there is a wider choice of colors on the EGA.

Both the EGA and CGA support a special BIOS call to allow you to choose between using the LIGHT modifier for background colors and the BLINK modifier for foreground colors. The default setting of the EGA has blink enabled, as in the CGA, and accepts the same logical attribute definitions as the CGA.

The discussion here assumes that the EGA is operated with its default settings, so it behaves like a CGA. Vermont Views does not provide special support for the EGA. If you modify the default settings of the EGA, you are responsible for adapting the attribute definitions to fit the settings you choose.