3 Application Interfaces
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If the USB function is not used, you are advised to reserve test points for easy log capture
and software upgrade.
3.3.2 UART
Background
UART is a Universal Asynchronous Receiver/Transmitter. It converts a parallel input signal
into a serial output signal. UART is generally used to communicate with PCs, including
monitoring debuggers and other devices, such as EEPROM.
Schematic Diagram Design
The module has main serial ports MAIN_UART and AUX_UART, and debugging serial port
DEBUG_UART.
⚫ MAIN_UART supports baud rates of 1200bps, 2400bps, 4800 bps, 9600 bps, 19200 bps,
38400 bps, 57600 bps, 115200 bps, 230400 bps, 460800 bps, 921600 bps, 1000000bps,
1500000bps and 2000000bps. The default baud rate is 115200 bps, used for data
transmission and AT command exchange. Sleep and wakeup are supported.
⚫ AUX_UART is a set of auxiliary serial ports that can be configured as UART6 or UART3. It
supports baud rates of 1200bps, 2400bps, 4800 bps, 9600 bps, 19200 bps, 38400 bps,
57600 bps, 115200 bps, 230400 bps, 460800 bps, 921600 bps, 1000000bps, 1500000bps
and 2000000bps. The default baud rate is 115200 bps.
⚫ The debugging serial port DEBUG_UART supports 2000000bps baud rate for module AP
log output. The baud rate is 2M.
The serial port level of the MG661 module is 1.8V. If the level of the customer host system is
3.3V or others, it is necessary to add a level converter in the serial port connection between
the module and the host. The following figures show the design of reference circuit of the
serial port level conversion chip. You can design the input and output circuits of the dashed
line part by referring to the solid line part in the figure 15, but pay attention to the connection
direction.
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