User Guide

GM500-U1G_A

Hardware Development Guide

Figure 2–15Reference Circuit of USB Communication between module and AP

 When USB is not the desired function, connect differential signal, power and GND via test points. We recommend to connect

these pins to the standard pin header in order to convenient for debugging and upgrading.

Figure 2–16 Reference circuit of USB when

USB is not the desired function

Note:

we recommend connecting the USB interface for update and debugging the module.

we recommend connecting a 0 ohm resistor between module and AP, and placing 0 ohm close

to the module pin.

In order to ensure the USB interface design corresponding with the USB 2.0 specification, please comply with the following

principles.

It is important to route the USB signal traces as differential pairs with total grounding. The impedance of USB differential trace is

90ohm.

Pay attention to the influence of junction capacitance of ESD component on USB data lines. Typically, the capacitance value should

be less than 3pF.

Do not route signal traces under crystals, oscillators, magnetic devices and RF signal traces. It is important to route the USB

differential traces in inner-layer with ground shielding not only upper and lower layer but also right and left side.

Keep the ESD components as closer to the USB connector as possible.