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PCA9555: Output Inversion

Julian Chen
Expert 2550 points
Part Number: PCA9555
Other Parts Discussed in Thread: TCA9555

Hi E2E,

1. Could you kindly let us know PCA9555 output can be inverted by hardware method?

2. Did we just only set reg 0x04 and 0x05 to inverted the output?

Thnaks!

  • 0
    TI__Guru 62910 points

    Hi Julian,

    You may want to consider the newer p2p device TCA9555 over PCA9555.  It has a few improvements in the design (such as support for lower voltages and less sensitivity to power ramp profiles).

    For either device, though:

     - The default state of an input pin (high or low) when undriven could be configured by external pull-up/pull-down resistances.

     - The polarity of a pin configured as an input can be toggled via registers 0x04 and 0x05.

     - The output state of a pin configured as an output can be configured via registers 0x02 and 0x03.  If you want to output a high level, you can write a one to that pin's corresponding bit.  If you want to output a low level, you can write a zero.  If you wanted to invert this externally you could use an inverter or FET buffer, but I think in most cases it would be easiest to just write the opposite value when the device is configured via I2C.

    Please let me know if that doesn't make sense to you or if you have further questions.

    Regards,
    Max