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The internal serial data lines are wired to the 3.5mm connector as follows: RX Data (Receive) Ring: TX Data (Transmit) Sleeve: Ground (GND) Cable Features & DIY Notes Compatibility: This same pinout is generally used for the QYT KT-8900D Go to product viewer dialog for this item. Go to product viewer dialog for this item.

The programming interface relies on three essential lines: Ground (GND), Transmit Data (TXD), and Receive Data (RXD).