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PCA9535: Can the Output port registers be edited before the ports are configured as outputs?

hemanth peruri
Prodigy 30 points
Part Number: PCA9535
Other Parts Discussed in Thread: TCA9535

The GPIO ports or "PCA9535RGER" are configured as Inputs by default and are to be configured as outputs based on application need. However default value on output pin when they are configured as outputs is "1" or a high, because the default value of output port register is "FF". 

However in out particular application, there is a need to have default low or "0" on the pins from the moment they are configured as outputs. The approach we are planning to accomplish this is to "Write Output port register with "00" before configuring the port as output"

Is it possible or is there any restriction on writing the output port registers when the device pins are configured as inputs?

  • 0
    TI__Guru 74871 points

    Hi Hemanth,

    The way you have described is how I would recommend you approach this. You should set the output register values first THEN go to set the configuration register to be an output. That way the pin of interest won't immediately drive HIGH after enabling the pin to be an output.

    One small tidbit, I would recommend the TCA family (TCA9535) if possible. The TCA line up supports wider Vcc ranges, uses newer process technology, and resolves some of the issues the PCA family had. (PoR restrictions lightened and INT errata resolved)

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 30 points

    Thanks Bobby for quick response,

    I am trying to get a confirmation regarding the accessibility to output port register during the time GPIOs are configured as inputs. If you can confirm that output port registers can be write accessible irrespective of the configuration port registers, I can consider my issue is resolved.

    Thanks for suggestion regarding TCA family of devices, I can consider this series for further procurement as long as the devices are pin compatible.

  • 0 in reply to hemanth peruri
    TI__Guru 74871 points

    hemanth peruri said:

    Thanks Bobby for quick response,

    I am trying to get a confirmation regarding the accessibility to output port register during the time GPIOs are configured as inputs. If you can confirm that output port registers can be write accessible irrespective of the configuration port registers, I can consider my issue is resolved. [Bobby] Confirmed.

    Thanks for suggestion regarding TCA family of devices, I can consider this series for further procurement as long as the devices are pin compatible.