Abstract: In a data processing system, an input line voltage is provided to a series voltage regulator which, in turn, provides well defined DC voltages to various logic devices including a system controller, such as a microprocessor. System controller operation is degraded by variations in the DC voltage provided thereto, generally resulting in the erroneous writing of data into a nonvolatile memory in the data processing system when the DC voltage provided to the system controller drops below a given voltage level caused by, for example, variations in the input line voltage. The input line voltage to the data processing system is monitored across the series voltage regulator for deselecting/write disabling the memory in the event the input voltage drops below a predetermined level, such as due to power transients, to prevent loss of data stored in the memory.

Abstract: 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.