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NRST signal connection

Sujata Yadav
Prodigy 30 points
Other Parts Discussed in Thread: LP55281

Dear sir,

I am using TIS LP55281 in our product with I2C communication.

In the datasheet

1) Typical application connection diagram does not mention any connection for "NRST" pin. can I left this pin un connected in my design? Will the IC get proper reset?

2)   "Modes Of Operation" section  on page 8 mentions about  RESET as "The LP55281 can be reset by writing any data to the Reset Register (address 60H). " Does this means that even I left the NRST pin unconnected and write random value at 60H will reset the module? I want to understand, before I write at address 60H using I2C, in what state LP55281 is? 

3)Please confirm, whether writing at address 60H will bring chip in reset state after powering oN my device or it will reset the chip at any point during its normal operation?

4) The block diagram shows connection of LP55281 with microcontroller, here along with I2C lines , NRST is also connected to MCU. Why?

As NRST is active low, does this mean that we have to connect this pin to provide reset signal at power ON.

5) It will be great if you can share some code for I2C interface of LP55281 as an example.

6) Please confirm whether, NRST should have connection for Active low signal or only writing to address 60H will provide reset to pin?

Regards,

Sujata

  • 0
    Prodigy 30 points

    Hi All,

    Can anyone update on this this issue?

    Thanks in advance.

  • 0 in reply to Sujata Yadav
    TI__Intellectual 2090 points

    Hi Sajata

    NRST should either be connected to system MCU or VDDIO but can't be left floating.

    The device is RESET by NRST or POR or Reset Reg (I2C write to 60h).

    POR only occurs at power up, if you need system reset without power cycle you will need to use NRST or Reset Reg.

    Randy

  • 0 in reply to Randy Dahl
    Prodigy 30 points

    Hi Randy,

    Thanks for your answer.

    In my hardware design, I have left the NRST pin floating. I am facing some issues to communicate with RGB controller.

    As per your inputs, With my current hardware the way to communicate with RGB is to use POR and reset the RGB controller using RESET Reg in firmware when required.

    Please find my hardware design below and let me know it is suitable for for POR and Reset through RESET Reg.

    Many thanks for your inputs.

     

    Regards,

    Sujata


  • 0 in reply to Sujata Yadav
    TI__Intellectual 2090 points
    Hi Sujata

    NRST can't be left floating as it will keep the device in RESET mode.
    The reset mechanism is an OR condition so any one of the three will put the part in RESET mode.
    In this case NRST will override both POR and RESET Reg.

    Best regards,
    Randy