What happens if SA0 is left unconnected on MMA8451Q?

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What happens if SA0 is left unconnected on MMA8451Q?

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Contributor I

I accidentally left SA0 of an MMA8451Q on my latest board. What type of behaviour can I expect? I would assume that it either defaults to one adress (0x1C or 0x1D), is the adress determined at startup (i.e. it randomly choses one adress, but sticks to it as long as it has power) or will it continuously jump between the addresses?

The first and second scenario can easily be handled in software, but the third will be a bummer.

Thanks,

Edit: AN4077 states "Pin 7 (SA0: Address Pin), ... should all use pull-up/down resistors to ensure they maintain the state of the pin.", so I assume leaving it unconnected was a bad move.

Message was edited by: osed

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TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Oscar,

Yes, the SA0 pin does not have an internal pull-up or pull-down resistor, so there is no way to know what value will be at the pin if left floating. It is required that the SA0 pin be connected to VDDIO (7-bit address = 0x1D) or GND (7-bit address = 0x1C).

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct". Thank you.

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TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Oscar,

Yes, the SA0 pin does not have an internal pull-up or pull-down resistor, so there is no way to know what value will be at the pin if left floating. It is required that the SA0 pin be connected to VDDIO (7-bit address = 0x1D) or GND (7-bit address = 0x1C).

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct". Thank you.

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