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Teridian single-phase and three-phase energy meter integrated circuits have a variety of interconnect ports for data access and information display. This application note provides details on connecting liquid crystal displays (LCDs) to the 71M6511, 71M6511H, 71M6513, and 71M6515H devices. These details are relevant for demonstration cards 71M6511, 71M6513, 71M6515H with Varitronix VIM-808 mono LCD displays, but the general rules apply to all static and multiplexed LCDs. The article also details the LCD routines used in the demonstration board firmware.
Teridian Semiconductor's 71M651x has a variety of interconnect ports for data access and information display. This application note was developed to provide details on the interface of LCD screens to the 71M651x chips.
LCDs use voltage-sensitive organic molecules with a helical structure that block or allow the passage of polarized light. The filled areas of molecules that form parts of the screen are called segments or pixels. For an appropriate function, an alternating current (AC) must be applied to the segments. LCDs with only a few segments can be operated in static mode, ie each segment has its own cable or pin that is connected to an AC voltage source (controller). To keep the number of connections low, LCDs with medium or large density are usually operated in multiplexed mode, ie the individual segments share pins with others and the screen is activated by selecting a group of segments for a short period of time and Then Moving on to the next group. The inertia of the organic molecules in one segment keeps the segment "ON" while the driver is accessing another group of segments.