I use LIS3DH accelerometer. For some reason pin 8 left open ( not connected) I use I2C protocol, and it works. any exploitation how it works ( pin 8 should be tied high for I2C), Pin 8 : CS : "1" - I2C , "0" - SPI Thanks

[OWigd.1]

..

[Eleon BORLINI]

Hi @OWigd.1​ , it's not a totally safe condition leaving Pin8 unconnected, since it is by default an input high impedance node. Is it working I2C only sometimes or always? Regards

[OWigd.1]

Hi
Its working I2C all the time.
I have lots of such boards in the field , and I need
A good excuse not to recall !!!
Thanks

[OWigd.1]

Hi Eleon,

Thanks for your answer.

Yes, i know it not "totally safe"

But is there an explanation why it works well for me ( I2C) and never wakes up SPI mode ?

Are you familiar with the HW design of pin8 (CS) input ?

Thanks

[Eleon BORLINI]

Hi @OWigd.1​ , what I understood from our experts is that the CS is high impedance to be properly driven but the device sets internally a status (i.e. like an internal pull-up) to prevent a wrong or unknown startup status in the case the pin is not connected. Btw, I confirm again that this pin should be connected at least to the application processor to be able to manage it in a known status. Regards

[OWigd.1]

Thanks Eleon,

This is important information for us.

So, to my understanding , If Pin8 ( CS) left open (I know I should be tied high for I2C)

LIS3DH shall establish I2C communication regardless ( this is what we actually see)

Could you elaborate more about : "but the device sets internally a status (i.e. like an internal pull-up) to prevent a wrong or unknown startup status in the case the pin is not connected"

A more technical / design explanation ( from the experts , chip designer) would be appreciated .

Regards and many thanks

Oded