USB communication circuit

 　　The function of the USB communication circuit is to realize communication between the device side and the host side of the data acquisition system. This function is mainly implemented by the core microcontroller ATmega16 and the USB control device PDIUSBD12 . Among them, PDIUSBD12 is a chip that complies with the USB1.1 protocol and plays the role of a bridge between the device and the host in the USB communication circuit. The microcontroller ATmegal6 and the USB controller PDIUSBD12 communicate through an 8-bit parallel bus. The 8-bit parallel bus needs to connect 8 I/O ports on the ATmegal6 side. PDIUSBD12 integrates a clock multiplication PLL on-chip, and the crystal oscillator circuit uses a 6MHZ crystal oscillator and two capacitors from 2pF to 68pF. A 18 ohm matching resistor must be connected in series to the signal output terminals D+/D- of PDIUSBD12 . The communication circuit is shown in Figure 2.