That's always drove me nuts because the underlying issue is a great idea, frustrated by its implementation. The serial port serves dual-purpose. Along-side th

That's always drove me nuts because the underlying issue is a great idea, frustrated by its implementation. The serial port serves dual-purpose. Along-side the obvious serial, you can also provide some inputs by grounding certain pins, and some outputs by sinking current from others. This has got me through some unorthodox integrations by having the UPS signal that it's on battery by having these "simple signals" close a contact/relay on the load. It's not quite a full suite of dry contacts, but it's pretty serviceable. The problem is that 9 pins doesn't leave many spare, so to achieve this they've repurposed some. I really wish they'd implemented this as an alternate mode so you'd, for example short tx to rx to change the behaviour - instead of having the 'alternate behaviour' sitting on standard DTR/RTS pins. Getting industrial interfaces at SOHO prices was awesome. The unintended consequences .. less so.