Hi fdebrus,
I wanted to give you a full update on everything we have done since your last messages, and also take a moment to express how much your support means to us.
Following your diagnosis of the corrupted frame ($1A vs $1E — a single-bit flip), we ran a series of tests to isolate the root cause:
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Direct cable test (laptop + 15cm RJ12, bypassing all house wiring): no frames received at all during passive listening, even with a dozen button presses. The PC-Link LED blinked on every press, confirming the bus was active. This ruled out the structured cabling as the culprit.
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Pinout change on the DB9 screw-terminal adapter: we swapped TXD and RXD as per your pinout table. Loopback confirmed the chain was electrically healthy. Still no passive frames received.
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Native DB9 serial port on the server: we attempted to pass through the server's onboard ttyS0 to the HAOS KVM VM, but QEMU/HAOS silently ignored the ISA serial device — it never appeared in the VM.
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Raspberry Pi 3 with direct USB connection (no KVM, no passthrough): we flashed a fresh HAOS on an SD card, installed Nikobus-HA v1.0.0, connected the PL2303 directly to the Pi 3, and tested. The result was identical to the KVM setup: NikobusTimeoutError on every command, and the same length mismatch ($1A16BB24... instead of $1E16BB24...).
This last test was the decisive one: with the PL2303 connected natively (no virtualization layer), we still get the exact same single-bit flip. This conclusively rules out KVM/USB passthrough as the cause and points directly at the PL2303 itself.
Based on your earlier analysis — that a clean single-bit flip points to UART sampling issues at the PL2303's input — we have ordered a genuine FTDI FT232R adapter (FTDI US232R-100, ordered from Farnell, expected within 72 hours).
This project has been going on for a while and I have to be honest: integrating my Nikobus installation (installed around 2004, ~40 circuits, 30 push buttons) into Home Assistant is something I really care about. Having my 20-year-old wired home automation system talk to modern HA would be incredible. Your patience, expertise, and detailed analysis have been invaluable — the bit-level diagnosis of that corrupted frame was frankly impressive and gave us a clear direction when we were running out of ideas.
We will report back as soon as the FTDI adapter arrives and we have test results.
Thank you so much for everything, fdebrus. This community is lucky to have you.
Jean