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Suggestion for improvement of TCA6408A and similar devices...

Soren Steen Christensen
Genius 3685 points
Other Parts Discussed in Thread: TCA6408A

Hi TI Logic support,

If you ever consider creating a TCA6408B version of the current TCA6408A chip (and other chips in the same family) I would hereby suggest you to add the possibility to do interrupt masking on individual IOs.

Currently it's unfortunately not possible to mask interrupts on (individual) input pins. By adding a simple mask-register and AND/OR'ing this to the actual input pin value this feature would easily be implemented, and as well be easy usable/programmable seen from a software point of view... :-)

Currently a "floating" input pin connected to a TCA6408A will have the posibility to create several thousand interrupts per second, which might cause trouble (or at least a lot of extra load) in software handling of control of the interrupt line, and currently there is no way to avoid such a condition other than making sure it won't happen (HW-wise), which requires addition external logic and thereby increased BOM and PCB size...

I hope you will seriously consider adding this easy/cheap enhancement to the product family for the future?

Best regards and thanks
   Søren

  • TI__Genius 9085 points

    Hi Soren!

    It's great to get feedback from the field like this, and I appreciate you taking the time to share your thoughts on our devices. I agree this could be a very useful additional functionality in certain applications.

    I've passed it along to the rest of the team here. 

     - Hattie

  • in reply to Hattie
    Genius 3685 points

    Hi Hattie,

    Sorry for not getting back to you prior to now, but the last couple of weeks have been pretty busy. Thanks for your quick reply and for taking my input forward to the design team. It's highly appreciated. A couple of further "easy" achievable ideas for improving the TCA64xx-series even further:

    1. Make it possible to have the ADDR pin floating or following the SCL/SDA-pin (used on some of the DAC/ADC AFAIR) to make it possible to use up to 3 or 4 devices on the same bus (as opposed to the current limit of 2 devices which is just on the edge). Maybe even as well introduce a new I2C-register for setting the device address to whatever the user likes after initial boot up. By keeping devices in reset until configured the user might then expand use like 10-20 devices in case they like... :-)
    2. Introduce a new register saving the reason that an interrupt happened. Today you will get an interrupt if an input line changes state. If it however changes back to initial state prior to SW getting time for serving the interrupt you will have no way to figure out why you got the interrupt request. By introducing a register which only get bits set/cleared from one interrupt until it has been served/read you will better be able to track (and react to) even short pulses on an input pins... :-)

    Should I weight the different additions I would like to see, I would judge them as:

    • Possibility to mask input pins form making interrupts: 65%
    • Possibility to have more devices on a single bus: 25%
    • Tracking interrupt reason(s) in special register: 10%

    Best regards and thanks again for your support
      Søren