The most common function of the USB data cable is data transmission and charging, and other structures are rarely known. Let's explain the more comprehensive USB data line structure knowledge:
USB data cable
USB data cord structure: consists of ground wire, power cable, D+, D- four wires, D+ and D- are differential input wires, which use 3.3V voltage (note that it is different from CMOS 5V level) The power and ground lines can supply 5V to the device, and the maximum current is 500MA (can be set in the programming, as far as the hardware implementation mechanism is concerned, leave it alone).
USB data format: Like other, USB data is composed of binary digit strings. First, the numeric string constitutes a domain (there are seven kinds), the domain reconstitutes the packet, and the packet constitutes a transaction (IN, OUT, SETUP), and the transaction ends. Composition transmission (interrupt transmission, parallel transmission, bulk transmission, and control transmission).
USB data line encoding scheme: USB uses non-return to zero to transmit data. When the differential data on the transmission line is input to 0, it is inverted. When inputting 1, the original value is kept. In order to ensure the accuracy of signal transmission, when it is in USB When a packet is sent on the bus, the transmission device performs a bit insertion operation (that is, inserts a 0 after every 6 consecutive 1s in the data stream), thereby forcing the NRZI code to change.
Also, the data is transmitted from the low to the high bit in the USB data line.
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