That’s a really interesting find. The Dr Smart Inverter Diagnostic Tool video changes how I’m thinking about some of this.
Up until now, I’ve been referring to the bus in my system as “S-Comms,” but based on what’s shown there, it’s possible what I’m seeing is actually PQE (non-S communication) over S1/S2. I hadn’t considered that distinction before.
For context, I’ve been working on a passive sniffer for the S1/S2 lines to monitor inverter behavior (separate from XYE control). The goal isn’t control — just visibility into real operating metrics. I have my current progress documented here if anyone is curious.
What really caught my attention in that video is the use of the “test port.” If that port is consistently populated across these units and operating at a 5V logic level (as suggested for non-S communication outdoor units), that could be a much cleaner and safer place to monitor traffic.
Compared to tapping directly into S1/S2 — where many installations have mains voltage present and significant noise/spikes — a 5V diagnostic interface would be a major improvement for safe, local sniffing.
I haven’t physically scoped the test port yet, so this is still theory. But combining:
- Passive monitoring via a low-voltage diagnostic port
- Active control via XYE
…could potentially be a very robust solution.