| 摘要 |
In a microprocessor-controlled video display terminal, coded data is used to represent characters and attributes associated therewith. Each attribute byte has associated therewith a designated control function such as underlining, inverse video, blanking, dimming, etc. If each attribute byte is comprised of M bits and there are N different attributes available for display, where M>N, then some of the bits comprising the attribute byte are not used. These unused bits are used in the present invention to represent a protected field in a character random access memory (RAM) for a given location, or address, on the video display and are read from an attribute RAM by the microprocessor for restricting access to the character RAM. In this manner, the writing of new data into selected portions of the video display is precluded.
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