[Coco] Detecting when CoCo is turned OFF

[Allen Huffman]

On May 7, 2021, at 1:59 PM, Salvador Garcia via Coco <coco at maltedmedia.com> wrote:
> 
> I am pondering on designing an Arduino based board to receive serial data coming from the CoCo's bit banger port. I would like for the Arduino board to do something when the CoCo is powered off and am thinking of ways to detect this event.
> The serial connection has four lines: CD, Gnd, Tx and Rx. I don;t see using any of these for this purpose, unless I missed something.

If you just mean having a way the CoCo can tell the Arduino it is shutting down, that is super easy with the serial port and a .99 cent TTL to RS232 adapter for Arduino.

If you mean a way to sense if it’s powered off, I do not know if those pins have any 5V when not in use. CD is an input, as is RX. I would expect TX to be low when not in use.

The Joystick has 5V at all times, doesn’t it? That would be a possibility, or noticing that there is RF be generated from the video output, perhaps?