LPWA Module Series
BG77 Hardware Design
BG77_Hardware_Design 39 / 76
A common mode choke L1 is recommended to be added in series between the module and customer’s
MCU in order to suppress EMI spurious transmission. Meanwhile, the 0
Ω
resistors (R3 and R4) should be
added in series between the module and the test points so as to facilitate debugging, and the resistors are
not mounted by default. In order to ensure the integrity of USB data line signal, L1/R3/R4 components
must be placed close to the module, and also these resistors should be placed close to each other. The
extra stubs of trace must be as short as possible.
The following principles should be complied with when design the USB interface, so as to meet USB 2.0
specification.
It is important to route the USB signal traces as differential pairs with total grounding. The impedance
of USB differential trace is 90
Ω
.
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 on not only upper
and lower layers but also right and left sides.
Pay attention to the influence of junction capacitance of ESD protection components on USB data
lines. Typically, the capacitance value should be less than 2pF.
Keep the ESD protection components as close to the USB connector as possible.
1. BG77 can only be used as a slave device.
2. The input voltage range of USB_VBUS is 1.3V~1.8V.
3.11. UART Interfaces
The module provides three UART interfaces: Main UART, Debug UART and GNSS UART interfaces.
Features of them are illustrated below:
The Main UART interface supports 9600bps, 19200bps, 38400bps, 57600bps, 115200bps,
230400bps, 460800bps and 921600bps baud rates, and the default is 115200bps. It is used for data
transmission and AT command communication, and supports RTS and CTS hardware flow control.
The default frame format is 8N1 (8 data bits, no parity, 1 stop bit).
The Debug UART interface supports a fixed baud rate of 115200bps, and is used for software
debugging and log output.
The GNSS UART interface supports 115200bps baud rate by default, and is used for GNSS data and
NMEA sentences output.
The following tables show the pin definition of the three UART interfaces.
NOTES
