Storing PWM Configuration on MLX90614 for MCU-Independent T

[MCUprogrammer]

I am trying to configure the MLX90614 thermal sensor to operate in PWM mode for temperature reading without an MCU. My goal is to write the desired PWM configuration to the EEPROM only once, so the sensor can retain this setting and run in PWM mode after power cycles. Specifically, I want to enable single PWM mode with either open-drain or push-pull output for direct temperature reading.

I think I'm making a mistake somewhere. I can't get it to work properly. Can anyone help me?

[Ttelmah]

Re read the data sheet.

On this chip you have to erase an EEPROM cell before you can write it.
Section 8.3.3 in the data sheet:

"Erase (write 0) must take place before write of desired data is made."

8.3.3.1

Gives the description of what has to happen. You have to write a zero,
wait 10mSec (5 min, but 10 is recommended), and hen write your new
data.

You have to do the clear operation before you can do the write. After
both, then power cycle the chip. You still have to perform this erase,
Even if the cell is already 0. It is like a lock mechanism. It'll only
accept the write of a value after a 0 is written.

[MCUprogrammer]

Firstly, thank you for your previous detailed explanation regarding the EEPROM write procedure. Based on your guidance, I applied the exact sequence: I performed the erase step by writing 0x0000, waited 10ms, then wrote the new value, and finally performed a power cycle. I understand that this process works like a lock mechanism, ensuring the chip only accepts new data after a proper erase. Could you please confirm if my implementation is correct or if I am missing any important details?

[Ttelmah]

Your PWM_CTRL address is wrong.

If you look, the address is 000xxxxx to talk to the RAM, or
001xxxxx to take to the EEPROM. You are writing to the RAM, not the
EEPROM......

The write should also be 16bits. Two 8 bit transfers. There should then be
a third transfer for the device to return it's PEC reply. Look at the example
write transfer.
Unlike 'normal' I2C, this device turns the bus round for this reply, so you do
a read without issuing another start.

[MCUprogrammer]

Firstly, thank you again for your detailed feedback on the PWM configuration process for the MLX90614. I’ve implemented the corrections you suggested, specifically:

EEPROM Access Correction:

I used 0x20 | MLX90614_PWMCTRL to ensure the EEPROM prefix (001xxxxx) is correctly applied, avoiding accidental RAM access.
16-bit Write Implementation:

The write sequence now transfers LSB and MSB separately as two 8-bit writes, complying with the 16-bit requirement.
PEC Handling:

I added the PEC values (0x6F for erase and 0xE1 for write) based on examples found in application notes.
However, I could not locate the exact reference for PEC value 0x6F in the datasheet.
If this PEC value must be dynamically calculated instead of hardcoded, I would greatly appreciate your guidance.

Does this updated code now fully meet the EEPROM write requirements?

Is the 0x6F PEC value acceptable, or should I calculate it dynamically?

After the write operation, is there any additional PEC verification step you would recommend for robustness?

[Ttelmah]

It doesn't use the PEC value on a write.
It actually sends it to you. It contains bits reflecting the status of the
chip itself.
Given that I2C is a wire or'ed bus (so doesn't mind two devices writing
at once), it is fine to just send the fixed value.
Touch wood it works.
Obviously SCL has to be held high for the PWM to work. Basically if
you send a clock on this, it disables the PWM, waiting for an I2C transaction.

[MCUprogrammer]

Thank you very much for your responses. 🙏

Based on your explanations, I have created the following structure. I did not include the PEC value and ensured that the SCL line remains high for the PWM to work.

If I load this code onto the board, I expect the PWM mode to function properly.

Did I understand you correctly? Is there any mistake or detail I might have missed in this setup?

Thanks in advance! 🌟
_________________
Best Regards...
MCUprogrammer
_______________________________
Work Hard

[Ttelmah]

It looks right.
Crossing things!.....

[MCUprogrammer]

Hi Ttelmah,

I’ve updated both the set_pwm_mode and clear_pwm_mode functions based on our previous discussions. My intention is to set the MLX90614 sensor to PWM mode and later clear it properly when switching back to I2C.

For set_pwm_mode, I’m first erasing the existing PWMCTRL value by writing 0x0000 and then writing the new 16-bit mode value, following the EEPROM write sequence in the datasheet.

For clear_pwm_mode, I’m simply clearing the PWMCTRL register by writing 0x0000 again, assuming this is enough to disable PWM mode and return to I2C communication.

My questions:

Does simply writing 0x0000 to the PWMCTRL register properly disable PWM mode and restore I2C functionality?
Am I using the correct EEPROM access prefix (0x20 | MLX90614_PWMCTRL) and addressing for the PWMCTRL register?
Are there any timing or sequence issues in my approach that I should be aware of?
Thanks again for your guidance!

Here’s the complete code:

[Ttelmah]

You won't be entering sleep mode.
To be in sleep mode, you have to hold the clock line low after sending
the command.
Sleep mode is only available on the 3v version. I never used this.

[MCUprogrammer]

This is the final version of the code then.

[MCUprogrammer]

After I put the MLX90614 sensor into PWM mode using this configuration, I plan to switch it back to I2C mode using the code above.

Do you see any potential problems with this approach?

Is there an additional step needed to ensure a smooth transition to I2C mode?