Restricted Attribute Handling

The ACUCOBOL-GT Terminal Manager assumes that video attributes can be applied individually to each character on the screen. This is the way most personal computers work with ANSI-conforming terminals. Several popular terminals, however, do not behave this way. This section discusses how ACUCOBOL-GT treats these terminals and what restrictions they impose.

Note: the rest of this section does not apply to MS-DOS or Windows implementations of ACUCOBOL-GT except those using the alternate runtime with a terminal database file. If you are a "standard" MS-DOS user and plan to move your programs to UNIX or VMS systems, you may want to read this section to familiarize yourself with the restrictions these environments impose.

Some terminals implement video attributes by a method that conflicts with the assumptions of the Terminal Manager. These terminals have special characters that show on the screen as a space, but set a display attribute for succeeding characters. That attribute is applied until another attribute-setting character is found. If one of these special characters is overwritten, its attribute is not set.

UNIX documentation calls these attribute characters "magic cookies." They are also sometimes called "non-hidden attributes." Two terminals that use this style of attribute handling are the Televideo 925 and the Wyse 50.

This type of terminal poses special problems. One issue is where to place the attribute character. If it is placed in the first location of the field, the data in the field is moved over one character position, resulting in a different display than on other types of terminals or personal computers. If it is placed just before the field, it might overwrite some valid data. Combining attribute characters with windows is even more intricate.

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Restricted Video Modes