MMA8451Q I2C maximum speed

[johncampbell]

It's stated on the first page of the Rev10 datasheet the following:

I2C digital output interface (operates to 2.25 MHz with 4.7 kΩ pullup)

Within Section 2.3 table 4 I2C (slave timing values) for SCL clock Low of 1.3 uS and SCL clock High of 600nS.

These are the minimum values.

This implies a maximum clock period of  1.9uS or a Clock speed of 526KHz if you use the minimum time allowed for high and low.

This doesn't correspond to 2.25MHz.

Question1:   What am I missing?

Question 2:   If my micro can support higher I2C rates what is the maximum clock I can run?

[david_diaz]

Hello John,

Thank you for writing.

In this case, the MMA8451Q supports the I2C Fast Mode, which means that the bidirectional data transfers can be made at up to 400 kbit/s.

The tHIGH and tLOW parameters, are the minimum time in order to perform a correct communication as shown in the image below.

So, the maximum clock you may run using your MCU as a master is 400 kbit/s.

Please let me know if my answer is clear.

Regards,

David

[johncampbell]

David,

Thanks for your response.

The timing is the standard timing found in the I2C specification.

I would still like to know why it states in the datasheet.

I2C digital output interface (operates to 2.25 MHz with 4.7 kΩ pullup)

Because of my microprocessor I2C eratta problems I need to develop a "bit bashed" I2C for the FIFO transfer.

This is why I am interested in the max clock speed I can achieve.

best regards johnc

[david_diaz]

Hello John,

My apologies for the delay.

Definitely, this is an error in the datasheet. Please rely on the specifications mentioned on table 4 from the datasheet and not on the features section in front page.

I hope this information helps.

Regards,

David

[johncampbell]

David,

Thanks.

I will adjust my speed to the maximum allowed by the timing in the table 4. (with some margin of course)

Regards johnc