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Decoding - initial thoughts

A project log for Reverse Engineering Grant ASHP Remote Protocol

Reverse engineering the protocol used by our Grant ASHP remote.

mjc506mjc506 03/27/2020 at 22:530 Comments

For now, I'll focus on the digital readings I took, as they're easier to play with...

Sigrok digital file

The above file is a ~30sec capture of the TX and RX (from the remote's point of view) pins on the T6B70BFG. As this is kind of a one-wire interface, everything transmitted is simultaneously received... The datasheet for the T6B70BFG mentions that the device will have to ignore its own transmissions.

It appears to decode as UART at 1200baud, 8N1 (although with large gaps between bytes)

think I can see an ack packet, but this will take some time to decode, as the data potentially includes many variables. However, RX'd packets are of differing lengths, so the ASHP is unlikely to be sending everything all the time - more likely is that the remote requests certain data, and the ASHP responds accordingly.

It is probably possible to work out TX packets reasonably easily, as I can control what the remote asks for, and perhaps then either match up RX packets with displayed data, or send my own data to the remote.

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