BNO055 not responding to UART

[manag]

Hello

We have a problem with an UART configuration.

We have an entire batch of 6 boards that have been designed as-per the following schematic (see both datasheet, and actual schematic) that does not work.

We provide a UART command using 115200 8N1, but the BNO055 COM0 pin (UART_RXD signal or P87 in our schematic) is always low. We have isolated that signal (cutting R361) to see if the MCU was driving it low, but both sides of the resistor read 0V even then.

In a desperate effort and to discard the microcontroller, I have isolated my on-board BNO055, and attached with 4 wires (VDD, GND, TX, RX and PS0/PS1 for UART) an Adafruit BNO055 board, and it answers to commands correctly.

What is wrong with my schematic? It is as per the latest BNO055 datasheet, as far as I am concerned. I notice that PIN15 and PIN16 are DNC, but I saw another appnote where they are tied to GND, and even in the Adafruit BNO055 board they are tied to GND (along with pin 10, which in my case is DNC), and the system works with this board.

Thank you

[manag]

We have a problem with an UART configuration.

We have an entire batch of 6 boards that have been designed as-per the following schematic (see both datasheet, and actual schematic) that does not work.

We provide a UART command using 115200 8N1, but the BNO055 COM0 pin (UART_RXD signal or P87 in our schematic) is always low. We have isolated that signal (cutting R361) to see if the MCU was driving it low, but both sides of the resistor read 0V even then.

In a desperate effort and to discard the microcontroller, I have isolated my on-board BNO055, and attached with 4 wires (VDD, GND, TX, RX and PS0/PS1 for UART) an Adafruit BNO055 board, and it answers to commands correctly.

What is wrong with my schematic? It is as per the latest BNO055 datasheet, as far as I am concerned. I notice that PIN15 and PIN16 are DNC, but I saw another appnote where they are tied to GND, and even in the Adafruit BNO055 board they are tied to GND (along with pin 10, which in my case is DNC), and the system works with this board.

Thank you

[BSTRobin]

Hello manag,

Could you confirm you schematic is this?

[BSTRobin]

Hello manag,

We had checked schematic was ok, and reference boards worked well.

Suggestion for you: 1.Check your HW PCB, welding; 2. Directly use USB to uart tool to connect UART RX, TX of your HW board, and send command like previous reply we sent.

[manag]

Hello

RX pin is always in low level (even detached from the MCU) so we cannot test them externally. Also, external XTAL won't crank up.

We will check welding as a last resort, otherwise we believe it's a bad batch of BNO055s that we got.

[BSTRobin]

Hello manag,

No external crystal oscillator is required by default, and it can work with internal clock.

Do you have distributor? If yes, you can put the chip on the socket and test it.

[manag]

Hello

We removed XTAL and capacitors from one defective unit, and still the same outcome.

We bought them from retail (Mouser), so we don't have that option.

Adding the shortage of chips (35W lead time), we are in a very tricky situation right now.