Microcontroller with LCD control over updating of RAM-stored data determines LCD pixel activation

摘要

Method and apparatus for controlling the updating of a random access memory (RAM) that stores data for coding the activation of segments of one or more alphanmeric characters of a liquid crystal display (LCD), to maintain substantially a direct current (DC) voltage value of zero across transparent conductive plates of the LCD, is performed or provided in a microcontroller having internal LCD control capabilities. A type B waveform is employed for activating the LCD, the waveform being of a type in which data is transmitted over two frames, the data in the second frame of which is the inverse of data in the first frame thereof to maintain an average DC voltage value over each two-frame portion of the waveform at substantially zero volt. The RAM is allowed to be written to for updating the data therein only after completion of an entire two-frame portion of the waveform and before commencement of a new two-frame portion, to avoid a non-zero average DC voltage across the LCD glass during a two-frame portion. An error bit is set whenever an attempt is made to write to the RAM at times other than between the end of a two-frame portion and the commencement of a new two-frame portion. A response to the error bit is made by returning to the write step that prompted it, to determine whether all of the data intended to be written has been stored in the RAM.