LCD module interference and ESD problems in finished systems

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This article explains LCD module behavior during system-level EMC/ESD testing: an LCD module is a passive input device without error correction - it accepts any timing-valid signal and cannot judge correctness, so wrong signals produce wrong commands or images; locate the interference source first, then eliminate, weaken or shield it. Measures: (1) no display and contrast unresponsive (an interference pulse on the power or /RESET line resets the module): add a 10 uF stabilizing capacitor plus a 0.1 uF or 0.01 uF filter capacitor between VDD/VSS near the module, or a 0.1/0.01 uF capacitor between /RESET and VSS, sized by test results. (2) Wrong characters, noise dots, image shift or flip, sometimes unrecoverable (interference on /WR, /RD, E or /CS control lines corrupts registers): shield with ferrite rings or foil, reroute and shorten the transmission lines, and add 100-300 pF capacitors to ground (VSS) on key signals - parallel mode in the order /WR(/RD) or E, then /CS, then RS; serial mode in the order SCLK, SDA, then RSRESET.