LP55231: About I2C communication when 0xFF is written to the reset register

Hi Kaji,

Could you check if every register's value is changed to default value successfully?

And could you attach the waveform of SCL/SDA?

Thanks!

Ives Li

Thank you for your reply.
I will check the contents.
However, I referred to the driver included in the Linux source tree, but it seems that ACK is not returned.
Please let me know your opinion on this.
Best regards,

github.com/.../leds-lp55xx-common.c

Hi Kaji, 

I'll test the SDA/SCL state during reset mode, and I will reply you the result later.

Thanks!

Hi Kaji,

Please see the RESET command SDA/SCLK waveform, and the ACK signal is on the waveform:

Thanks!

Thank you for your reply.

I checked the waveform and confirmed that ACK was returned. thank you.
As for the last question, when I check the Linux driver created by TI, I find the following comment in the lp55xx_reset_device function.
"/* no error checking here because no ACK from the device after reset */"
github.com/.../leds-lp55xx-common.c
With bootloader or Linux, is there a case where ACK cannot be picked up at Reset?
Please let me know your opinion on what the above comment means.

Best regards,

Hi Kaji,

It means that after the data was sent, the device will enter RESET mode and will not generate the ACK, and the last pulse of SDA you see in the wave form is pulled low because for the I2C STOP condition.

Thanks!

Thank you for your reply.

According to your answer, the last pulse is not ACK but STOP condition, but after checking the data sheet and I2C specification,
After the ACK there is a STOP condition and the STOP condition should only be generated from the master.
Therefore, it is unlikely that a STOP condition is generated without an ACK.
I think below.
LP55231 seems to return SDA to “H” immediately after receiving reset and generating ACK.
I think the reason for this is that the LP55231 executes a reset immediately after generating the ACK.
In your opinion, RESET does not conform to the I2C standard format, but please let me know your opinion.

Best regards,

Hi Kaji,

You can compare below 2 screen shoot:

1. send data to set PWM value:

2. send reset commend:

It seems for reset commend the device will not generate the last ACK

So, does this format bother you and affect your applications?

I can help you check the reset data format if necessary.

Thanks!

Thank you for your reply.
I understand your answer.
Finally, I would like to tell you that the datasheet does not describe the behavior of this reset.
Is the content separately described in an application report, etc.?
Best regards,