Protected Region Clearing

The 'CF' mnemonic in PRO/5 clears the high-intensity characters on the display while leaving all other characters intact. This is usually done manually by PRO/5 by printing spaces in every position on the screen that is known to contain a high-intensity character. While this operation is performed with acceptable speed, it is sometimes faster to use the terminal's built-in capabilities if they exist.

Many terminals have what is known as "protect mode" and "protected regions." There are "begin protected region" and "end protected region" sequences that may be used as characters are sent to the display to indicate what parts of the display are "protected." Later, if it is desired to clear everything but the protected regions, the application may send a "protect mode on" sequence followed by a "clear" sequence, followed by a "protect mode off" sequence. PRO/5 can use these sequences to protect all low-intensity characters so that a 'CF' mnemonic may quickly clear all high-intensity characters.

The following fields are used to define protected region capabilities:

Field	Description
Cy=	Sequence to turn on protect mode.
Cz=	Sequence to turn off protect mode.
Cx=	Sequence to clear all non-protected characters. This could be a simple "clear screen" sequence or a special protect mode clear sequence. It will always be sent along with the Cy= and Cz= strings.
Cw=	Sequence to clear non-protected characters from the cursor to the end of the screen.
MA=	Sequence to end a protected region.
MB=	Sequence to begin a protected region.

The :MA=: and :MB=: fields were described earlier to set and reset the high-intensity character attribute. It is these characters that are not to be protected (and cleared with the 'CF' mnemonic). If the MA= and MB= fields are used for high-intensity attributes, then they may also include the protect region sequences as part of the string. If other methods of specifying character attributes are used (the :AA: field or :Cp=:Cm=: fields), then :MA=: and :MB=: may be used for the sole purpose of providing protected region sequences and will be used by PRO/5 when displaying high-intensity characters.