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I'm trying to decode a serial protocol from my underfloor heating system (OJ Electronics)

Example of bus communication sent every 11s is quite small and looks like:

overview of communication

This will need to contain info like target temp, channel (0-14), demand on/off etc.

I'm not able to find a fit for baud/start/stop settings as keep getting frame errors. Best fit is defaults at 9600 baud. Any help in reading this appreciated.

Saleae capture

Equipment is Rehau WLM Master communicating over 2 wires at 5v with WL Thermostats.

Rincewind
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    I would suggest that the trace you show is NOT async 9600 baud. It looks like there is always a signal (the leading square wave) that is probably a crude operational flag. It then switches to an aync stream to send data, and then back to the operational flag at the end. This will confuse the serial protocol decoder on the LA. The only way to rectify this is to edit the capture. – Jack Creasey May 02 '22 at 13:18
  • thanks @JackCreasey, I'll try and chop the leading square wave off and see if it looks any better. There's actually about 11s of high signal before that which I didn't show. – Rincewind May 02 '22 at 14:08
  • You need to change the Google Drive access rights of your Saleae Capture file to _"Anyone on the Internet with this link can view"_. – Velvel May 02 '22 at 14:23
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    @Seir oops, updated – Rincewind May 02 '22 at 15:56
  • First of all, what makes you think it is async serial to begin with? If it is, you can likely determine the baud rate by determining the smallest stable bit period. Just use large enough sampling rate to avoid problems. – Justme May 02 '22 at 16:12

2 Answers2

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It is almost certainly not async.

The leading sequence of zeros and ones is a preamble for the receiver to synchronize its sampling.

The first byte is probably a sync word for the receiver to set the timing of the bytes.

The rest of the data is probably manchester encoded or similar with no gaps between bytes.

The last couple of bytes may be a CRC for error checking. It may not be 8-bit bytes.

There are a few standard protocols although it may be proprietary from the vendor. Here is one open standard:

Opentherm

Please give more details about the equipment.

Kevin White
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Maybe try some different settings in the "Manchester" decoder:

enter image description here

Solomon Slow
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