Rui Peng iFLYTEK: some security matters in the USB using
when we should pay attention to


1. the pull-up resistor of the high speed and full speed equipment is above the D+. The pull-up resistor of the low speed device is above the D-. After the high speed mode is connected, the pull-up resistor on the D+ is disconnected.
 
2., the MINI USB interface for USB OTG has 5 lines and one ID line for identification (host or slave).
 
3. in low speed and full speed mode, voltage transmission mode is adopted, and current mode is adopted in high speed mode.
 
4. in theory, a USB master can access up to 127 devices because the protocol specifies that each device has an 7bit address and that the 0 address is reserved for uninitialized devices.
 
5.USB is a master slave architecture, and USB data transfers are all hosted by the host.
 
6.USB to RS232 serial port, the data is not stable, if the computer motherboard hardware aging or lower anti-jamming performance, easy to lose data, or simply do not recognize the USB serial port, or interfere with other software programs, and require a restart to normal