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Hot!RN4871 not communicating with UART

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2020/05/31 21:18:39 (permalink)

RN4871 not communicating with UART

I've bought a RN4871, connected to Trinket M0 (Trinket M0 provides a power of 3.3V, TX, RX, and GND to RN4871 module). Since the datasheet has a reference circuit, it would be relatively simple to communicate through UART with the module.
The RN4871's user guide specifies the default UART settings as: baud rate: 115200, data bits: 8, parity: none, stop bits: 1, and flow control: disabled.
Unfortunately, it has been impossible to even start communication with the module through UART.
To make sure that Trinket's UART was working, I connected the Trinket to an Arduino Uno (through UART) with the same settings and the communication was successful.
Also, I coded the Trinket to blink an LED every time the Trinket's RX line changed. It appears that the RN4871 module does not even attempt to change the UART_TX line, since the LED never blinked. The LED blinked when the Trinket was connected to the Arduino Uno.
Also, driving the RST_N pin low does not appear to produce any effect (the reset pin was connected as in figure 5-4, page 27 of the datasheet).
Finally, I bought two modules (after the first one did not give any sign of life) and both are not working.
I would appreciate any suggestion on how to get the UART communication working. Note: I do not own the RN-4871-PICtail development board because: 1) it is too big for my application, and 2) the RN4871 datasheet made the connection look extremely simple, thus not being necessary a complete development board (see page 25 of the datasheet).

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