BNO055: should pins 15 and 16 be connected?

[SteveF]

We have just designed a board with BNO055 on it. As per the datasheet (Rev 1.7, Nov 2020), we left pins 15,16 "DNC" - unconnected.

On powering up the board, the BNO055 does not respond to I2C commands (no ACK to slave address).

We had previously prototyped the system using 3rd party BNO055 eval boards, and it worked fine.

The only difference we can spot is that pins 15 and 16 are connected to GNDIO on every eval board we can find.

We see the datsheet also used to have these pins connected to GNDIO, but it got updated in Rev 1.6, Feb 2020. There was a firmware update also just before this.

The ICs on our board may be several years old, so might it be possible that the older firmware in these does actually need pins 15 and 16 connected to GNDIO?

[BSTRobin]

Hello SteveF,

Have checked your schematic, except for the crystal part, the rest is the same as the reference schematic.
The I2C waveform of the shuttle board, as you can see, has I2C ack.

[manag]

Hello

We have the exact 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.

Can you provide any advice?

Thank you