RS485 bus

Haiwell and most VSDs: RTU, 9600, 8N1. Delta DVP as it leaves the factory: ASCII, 9600, 7E1. RTU needs an 8-bit format; ASCII is normally 7-bit.

DE release delay is how long the driver stays on after the last stop bit. Keep it small — 10µs suits this board. Too large and a fast slave (a Delta answers in well under a millisecond) loses the first characters of every reply, which reads as a timeout even though the device answered perfectly. Raise it only if the LAST character of what you send is being lost.
Raise the response timeout for slow VSDs and long cable runs. Add an inter-frame gap only if a device answers erratically — some cheap slaves need more silence than the spec demands.

Protocol, baud and format changes take effect on restart — the serial port only reopens on boot.

Probes each address for a reply, proving wiring, baud and format without needing to know a single register. A device answering “illegal address” still counts as found — it is there and correctly addressed, it just has no register 0. Results persist across a reboot and fill the Discovered picker on the Poll Map.

Tries every protocol, baud and format against that one address — 78 combinations, about 15 seconds — and saves whatever works. If nothing answers at any setting, the serial parameters are not your problem: look at A/B polarity, the signal ground, and the device’s own port configuration.

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One raw Modbus request straight to a slave, bypassing the poll map entirely. Use it to confirm an address before committing it to a block.

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The raw bytes of the last exchange. Bytes sent but nothing received means the request never reached the device or its reply never got back — wiring, polarity, ground or direction control. Bytes received that still fail means the device is talking and the framing or address is wrong, which is a much better place to be.