Low (small value resistor to ground or connection to ground) if you are connecting an accessory that the device must ask as a host for. The device with the 5-pin connector has a pullup to high on the connector. There are two variants of plugs: Micro-A connector and Micro-B connector and two variants of receptacles - Micro-AB (for both Micro-A and Micro-B connectors) and Micro-B. Micro-USB connectors, which were announced in 2007 have a similar width to Mini-USB, but approximately half the thickness, enabling their integration into thinner portable devices. See also newer Micro-USB 3.0 cable pinout. Contrary to popular belief, D+ and D- operate together they are not separate simplex connections. Half-duplex differential signaling helps to combat the effects of electromagnetic noise on longer lines. In USB data cable Data+ and Data- signals are transmitted on a twisted pair. NRZI (Non Return to Zero Invert) encoding scheme used to send data with a sync field to synchronise the host and receiver clocks. Micro-USB cable uses 4 shielded wires: two for power (+5v & GND), two for differential data signals (labelled as D+ and D- in pinout). May be N/C, GND or used as an attached device presence indicator (shorted to GND with resistor) The micro-USB connector is often used for portable devices charging (with micro-usb charging cable) or mobile devices data transfer (with micro-usb data cable). Nowdays Micro-USB competes with newer USB type C and Micro-USB 3.0.
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