[Coco] Detecting when CoCo is turned OFF

[Salvador Garcia]

 Hi Joel, sorry for the late response, other activities pulled me away. To answer your questions:
I am trying to sense change of state. I want the Arduino gadget to perform shutdown processes when the user powers down the CoCo.
I want the Arduino to do something without the CoCo explicitly sending it specific data or commands. rather, The Arduino should sense (detect) when the CoCo powers down.
Take for instance modern OSes that require that the user run a Shutdown process so that the OS closes correctly. The user needs to remember to run the shut down process. This is something I would like to avoid with the CoCo for this project.
In my case, I want the Arduino to sense when the CoCo is powered down to perform such closing processes. I don't want to depend on the user to run a "shutdown" program on the CoCo. 
I am further checking on detecting the lack of -12v, as others have suggested, but welcome all ideas. Checking -12v isn't as straight forward because the Arduino will fry if I feed it more than 5v and worse if the voltage is negative.
Thanks for the follow up and for your input. Salvador

    On Saturday, May 8, 2021, 10:31:02 PM CDT, Joel Rees <joel.rees at gmail.com> wrote:  
  I can't tell if you are clear as to whether you're trying to sense state or
change of state, or both.

Also can't tell if you want the CoCo doing something to tell the Arduino
it's up (active) or want the Arduino to be able to read the CoCo without
the CoCo sending it any data.

In particular, if you want the CoCo running some sort of watchdog timer,
you're going to either have to accept that the CoCo won't do this unless
you've loaded the watchdog code. Or you might need to modify your ROM.