USB Bit Stuffing – BIT STUFFING

In USB, bit – stuffing is a crucial processing mechanism, mainly used to ensure the synchronization of clock signals during data transmission. The following is a detailed introduction:

Significance: Bit – stuffing ensures the reliability of USB data transmission, so that the sender and receiver can maintain synchronization in the case of no separate clock line, and effectively avoids data errors caused by long – term unchanged level, which is of great significance to the stable operation of the USB system.

Purpose: USB adopts the Non – Return – to – Zero Inverted (NRZI) encoding method, in which the level does not change when the data is 1. If there are a large number of consecutive 1s in the data stream, it will lead to a long – term unchanged level, which is not conducive to the receiver extracting the clock signal from the data stream, and may cause errors in data sampling and interpretation. Therefore, bit – stuffing is introduced to solve this problem.

Implementation Principle: Before data transmission, the sender performs bit – stuffing processing on the data. Specifically, when encountering 6 consecutive logic 1s, a logic 0 is forcibly inserted to make the transmitted signal have a level transition, so that the receiver can adjust the clock frequency according to these level transitions to ensure the synchronization of data reception.

Processing Process: The data after bit – stuffing is serialized by the Serial Interface Engine (SIE) and then sent to the USB differential data line after NRZI encoding. At the receiving end, the SIE first deserializes the data, and then removes the stuffed bits, that is, when receiving 6 consecutive 1s, the 0 immediately following is automatically deleted, so as to restore the original data.