[Alan Anderson]

I'm sorry, but I don't understand. I recognize all the words, and the question should make sense, but things just don't add up.

I usually think of "COM port" as referring to a computer's serial port. Is that what you mean?

Where do you have "9 total" inputs?

Do not connect ground and +. That's a short circuit, and you'll trigger the Digital Sidecar's overcurrent shutdown.

The voltage on a computer serial port follows the RS-232 standard, and is not directly compatible with the TTL-level signals of the Digital Sidecar. You'd need a level translator such as the MAX232 series.